A well-financed lobbying campaign by prominent U.S. politicians and former officials on behalf of a designated terrorist organization is focusing new attention on the group and its influential advocates.

Supporters of the Iranian opposition group Mujaheddin-e Khalq, or MEK, have met with senior Obama administration ­officials to push for the organization’s removal from the State Department’s terrorist list and better treatment of its members at a camp in Iraq.

Public appearances on behalf of the MEK by such people as former New York mayor Rudolph W. Giuliani, former Pennsylvania governor Edward G. Rendell and former Obama national security adviser James L. Jones had already sparked an investigation by the Treasury Department into whether payments of tens of thousands of dollars to some of them violated anti-terrorism laws.

In recent weeks, new questions have been raised about whether private meetings, conference calls and other contact with officials at the State Department and elsewhere in the administration over the past year require the advocates’ registration as lobbyists or agents of a foreign entity.

Under federal law, advocates for foreign organizations are required to register as lobbyists and provide details about their clients and income. But the MEK supporters have not registered, which would require disclosing the amounts they are paid and the identities of officials with whom they meet.

The supporters argue that they are acting legitimately to facilitate U.S. policy decisions, which could make them exempt from registration requirements.

But scholars of lobbying regulations say the contacts with administration officials easily meet the definition of lobbying under the Foreign Agent Registration Act, a law that has sometimes led to criminal charges.

“The law applies to anyone engaged in political or lobbying activity — or even propaganda — on behalf of a foreign ‘principal,’ a term that is defined broadly,” said David Cole, a professor and expert on criminal and constitutional law at Georgetown University Law School. “It’s a very low bar.”

The new questions are the latest challenge for the MEK, which has been listed by the State Department as a terrorist organization since 1997 and was linked to the deaths of six Americans in the 1970s.

Trying to reshape image

The MEK has been campaigning for years to get off the terrorist list, including buying advertisements in The Washington Post and other publications. A federal appeals court has given Secretary of State Hillary Rodham Clinton until October to make a decision on whether to remove the group.

At the same time, the MEK and its advocates have been clashing with the Iraqi government over efforts to relocate 3,300 MEK members living in exile at a former Iraqi military base since the mid-1980s.

The MEK has enlisted some of the biggest names in U.S. politics and national security. In addition to Giuliani, Rendell and Jones, the group’s advocates have included former homeland security secretary Tom Ridge, former Vermont governor Howard Dean, former U.S. attorney general Michael Mukasey, former FBI director Louis Freeh, former Joint Chiefs chairman Hugh Shelton, former U.N. ambassadors John Bolton and Bill Richardson, and Mitchell Reiss, a former State Department official who has been among Republican president candidate Mitt Romney’s top foreign policy advisers since 2008.

Rendell, Giuliani and Mukasey were among 16 prominent former U.S. officials who flew to Paris for a pro-MEK rally last month. Also in Paris was Newt Gingrich, the former House speaker and Republican presidential candidate. In a video, Gingrich is seen bowing to the MEK’s co-founder. Afterward, Gingrich appealed for “decisive action” by the United States on the group’s behalf.

The MEK and its umbrella group, the National Council of Resistance of Iran, denied asking anyone to lobby for them

The dissidents “have not asked anyone in the United States to advocate for them, nor do they have any agents or lobbyists in that country,” said Shahin Gobadi, a spokesman. He said State Department officials had asked U.S. supporters to intervene to prevent a “humanitarian catastrophe” at the MEK’s Iraqi camp, and noted that more than 100 U.S. lawmakers have co-sponsored legislation to remove the MEK from the terrorist list.

Still, some of the MEK’s prominent surrogates have acknowledged accepting travel expenses from MEK-allied groups as well as speaking fees of $10,000 to $40,000 per engagement. Rendell has acknowledged accepting more than $150,000 in expenses from MEK supporters. Before he began speaking on their behalf, he says, he knew very little about the MEK.

The supporters, some of whom have acknowledged intervening on the MEK’s behalf with U.S. officials, say their motives are humanitarian. They say pro-Iranian elements in the Iraqi government have attacked the group’s followers since U.S. troops who had protected them left Iraq.

“A number of us are working with the State Department to facilitate the removal of the Iranian dissidents” from the MEK’s base in Iraq, Dean said in an e-mail response to a Post query. “Since this is an effort to facilitate U.S. government policy, it does not require any form of registration.”

None of the other participants responded to requests for comment.

Federal lobbying law defines a foreign “agent” as someone who acts “at the order, request, or under the direction or control, of a foreign principal, or of a person any of whose activities are directly or indirectly supervised, directed, controlled, financed, or subsidized in whole or in part by a foreign principal.” It covers activities that include acting as a publicity agency or political consultant or representing the interests of the foreign group “before any agency or official of the government of the United States.”

“The only defense would be if you can claim that you’re doing it on your own, unpaid,” said a retired senior U.S. official and expert on lobbying law, who spoke on the condition of anonymity to discuss hypothetical cases covered by the statute. “But if you’re getting money from the same group to make speeches, it’s pretty hard to make the case.”

Although the foreign agents act is often flouted in practice, “the fact that it’s a criminal statute shows how the government regards this kind of activity,” the former official said.

In addition to meeting with the MEK supporters, State Department officials have acknowledged that they have used them to relay messages directly to the MEK leadership to try to resolve what has become a dangerous standoff over the closing of Camp Ashraf, the former Iraqi army base northeast of Baghdad that has served as the group’s home in exile since 1986.

With the Iraq government vowing to close the camp by July 20, U.S. and U.N. officials are seeking to relocate its 3,300 residents to the grounds of what was once Camp Liberty, the former U.S. military base near Baghdad’s airport.

The controversy over lobbying is the latest wrinkle in an ongoing dispute over U.S. policy toward the MEK, whose name translates as “People’s Holy Warriors of Iran,” befitting its self-described status as the leading Iranian opposition group dedicated to overthrowing the country’s ruling mullahs.

Founded by Iranian students in the 1960s as a Marxist-Islamist movement, the group is accused of killing six Americans in terrorist attacks in the 1970s during its struggle to topple the U.S.-backed shah of Iran, Mohammad Reza Pahlavi. Some of its members participated in the takeover of the U.S. Embassy in Tehran in 1979 before the MEK broke with Iran’s new Islamic rulers and began attacking the regime with suicide bombings and assassinations. Many of the group’s leaders were captured, tried and executed.

MEK officials sought exile abroad, first in France and later in Iraq, where the group found common cause with Iraqi leader Saddam Hussein. The dictator provided the movement with a sanctuary — later dubbed Camp Ashraf — as well as weapons, tanks and other equipment. MEK troops fought against their countrymen during the eight-year Iran-Iraq war.

Connections to Iraq

MEK leaders officially renounced terrorism in 2001, but ties to the Iraqi dictator earned the group the hatred of Iranians and many Iraqis. In 2003, the U.S.-led invasion of Iraq left the group without its powerful sponsor and with few appealing prospects, unable to return to Iran and detested by the new Iraqi leadership. No other countries offered refuge to a group that, in addition to the terrorism stigma from the 1970s, had gained a reputation for cultlike behavior — MEK members at Camp Ashraf wear military clothing and adhere to a doctrine that requires mandatory divorce for married members as well as celibacy, enforced separation of the sexes and unquestioned allegiance to the MEK’s leadership.

“I see them as a cross between Hezbollah and the Branch Davidians,” said Karim Sadjadpour, an Iran expert with the Carnegie Endowment for International Peace. “It is legitimate to debate whether the MEK meets the Justice Department’s legal definition of a terrorist organization. But it is outright false to claim that they are a legitimate, democracy-minded opposition group with a wide base inside Iran.”

The group did possess two attributes that would eventually allow it to build a network of allies and friends. One was an extensive cash reserve, some of it donated by wealthy Iranians in the West, and the rest acquired from still-unknown sources, something MEK leaders decline to discuss. The other was a deep antipathy for the Iranian government, a view widely shared by many conservative Republicans as well as more hawkish Democrats.

The MEK’s appeal as a potential partner against Iran sharpened in 2002 when the group exposed the existence of a secret uranium-enrichment plant near the Iranian town of Natanz. Slowly, a small band of influential Americans began advocating direct U.S. support for the dissidents as a tool for undermining Iran’s government.

“What’s the answer? Regime change,” said Ridge, the former homeland security secretary, in a speech on behalf of the MEK in late May. “The heart of this effort, we all believe, is to recognize democratic opposition — it is the MEK.”

Rendell and other MEK supporters also have acknowledged that their advocacy has attracted the attention of federal prosecutors. Since the spring, Treasury Department officials have interviewed several of the group’s supporters to determine whether they violated U.S. law by providing support to an organization on the U.S. terrorist list. A Treasury spokesman, John Sullivan, said the department does not comment on “potential investigations.” Other U.S. officials familiar with the group said the inquiry remains essentially on hold while awaiting a formal decision on the MEK’s terrorist status.

“The MEK is a designated terrorist group,” Sullivan said. “Therefore, U.S. persons are generally prohibited from engaging in transactions with or providing services to this group.”

State Department view

Depending on events at Camp Ashraf, the MEK could soon lose its terrorist label. Clinton told Congress in May that the State Department would look favorably toward delisting the group if it complies with U.N. efforts to relocate its members in Iraq to new temporary quarters.

More than half the members have completed the move, but transfers of the remaining 1,200 have stalled amid complaints from the MEK about poor conditions and mistreatment by Iraqi officials. MEK leaders are balking at sending additional convoys to Camp Liberty, having apparently calculated that their Washington advocates can secure better terms for them.

In recent days, tensions between Iraqis and MEK officials have escalated, raising fears that the situation could turn violent if the exiles refuse to vacate Camp Ashraf by the July 20 deadline, U.S. officials say.

“The great tragedy is that people who say they want to help the MEK have instead emboldened their sense of entitled status, and that could get them into serious trouble,” said a senior State Department official involved in MEK policy discussions. The official spoke on the condition of anonymity because he was not authorized to publicly discuss the matter.

“If the supporters want to save lives, they could do the MEK a great service by getting them to focus on real issues and not stage extravagant provocations,” the official said.

Joby Warrick and Julie Tate,