POLITICIANS cashing in as soon as they leave office may be the world's second-oldest profession - and, arguably, it's a job that nobody does better than Pennsylvanians.

Consider ex-governor and ex-Homeland Security chief Tom Ridge, who became a paid director of Home Depot a few years after his Department of Homeland Security urged Americans to stock up on duct tape.

Or Rick Santorum, ousted senator-turned-presidential candidate - a career politician who recently has earned as much as $1 million a year, some of it consulting for companies whose agendas he fought for in Congress.

But did Ed Rendell, the former governor who left office just l4 months ago, take it too far by taking big-time speaking fees and making multiple trips to Paris to advocate for an Iranian group that long ago called the United States "this satanic force threatening the world" and is still listed as a terrorist organization by the U.S. State Department?

An obscure arm of the U.S. Treasury Department is now looking into exactly that. Its Office of Foreign Assets Control recently subpoenaed records about Rendell's speaking fees on behalf of the militant group, Mujahedeen-e-Khalq, or MEK.

Rendell is one of a large number of ex-pols and ex-generals who've been paid by MEK and have advocated for the group - which opposes Iran's current rulers - to be removed from the terrorist list. But he's believed to be the only one whose fees are under investigation.

"The governor isn't going to comment, because it's an ongoing legal issue," his spokeswoman, Kirstin Snow, said yesterday. Over the weekend, Rendell left a lengthy voice mail with an Inquirer reporter in which he said that he felt "passionate" about the plight of the group, which says that its camp in neighboring Iraq has been attacked by the Iraqi government.

MEK dates back to the late 1960s, when it was a virulently anti-American, Marxist-Islamist group supporting an "armed struggle." But it turned against Iran's mullahs and was given shelter in Iraq - by its former dictator Saddam Hussein.

In 2001, MEK renounced violence and has not been linked to any attacks in recent years, although groups like Human Rights Watch still brand MEK as a kind of cult.

"They have somehow learned to exploit the twin weaknesses in the U.S. political system: the ignorance of the international affairs (in a world where all politics is local) and the ability to buy politicians with barely legal bribes in the form of 'speaking fees,' " Ahmad Sadri, professor of Islamic-world studies at Lake Forest College in Illinois and a critic of MEK, wrote in an email to the Daily News yesterday.

According to a 2011 article in the Christian Science Monitor, Rendell was asked by MEK to speak last July and declined at first - "I don't know hardly anything about this subject," he told them - but then changed his mind.

The Philly Democrat told the newspaper that he had been paid $20,000 for a 10-minute speech in which he said he would urge President Obama and Secretary of State Hillary Clinton to guarantee the safety of MEK's camp in Iraq.

He told the Inquirer that he was moved to back MEK in part because of its outspoken support from his GOP predecessor as governor, Ridge. It's not clear how many among MEK's legion of high-level supporters - not just Rendell and Ridge but former presidential hopefuls Howard Dean, Bill Richardson and Rudy Giuliani, and ex-U.N. Ambassador John Bolton - are paid for their efforts, and if so, how much.

There are other benefits for Rendell. He reportedly has been to Paris, MEK's headquarters, four times and to Geneva twice - all on behalf of a group he knew little about eight months ago.