“If I’m corrupt, it’s because I take care of my district.”

So said Rep. John P. Murtha , D-Pa., in a weekend interview with a home-state newspaper. What he was trying to convey was that the only thing his critics can complain about is his success in directing federal dollars to his district — if “taking care of” his district is a bad thing, well, then, he’s all for bad things.

It’s a classic example of setting up a straw man.

Murtha’s critics aren’t opposed to his ability to bring home the bacon; as the chairman, and then ranking member, and then chairman again of the House Appropriations Defense Subcommittee for the last two decades, Murtha’s control over the Pentagon’s purse strings is legendary, and the torrent of cash he has directed back to his 12th District makes the Johnstown Flood look like a spring drizzle.

His critics don’t begrudge him his pork. But they are questioning how close he has come to the line of ethical propriety.

And it’s fair to ask whether Murtha remembers any of the lessons he learned during that big of unpleasantness known as Abscam.

In the fall and winter of 1979-80, FBI agents posing as Arab sheiks tried to lure corrupt members of Congress into accepting hundreds of thousands of dollars in bribes in exchange for helping the faux sheiks get around U.S. immigration laws. The “Arab Scam” — Abscam — led to the convictions of five members of the House and one senator.

For his role, Murtha was given the same ignominious label attached to Richard M. Nixon in the Watergate scandal: “unindicted co-conspirator.”

Murtha refused to personally reach into a desk drawer and remove $50,000 cash, and insisted instead that a middleman take possession of the booty. When the FBI agent refused to agree to that arrangement, they agreed to meet again (at which point, the FBI agent hoped, Murtha would feel comfortable enough to take the cash himself). But before that second meeting could take place, the news media exposed the FBI sting operation, and Murtha agreed to testify against his congressional colleagues. After his testimony helped secure convictions, the Justice Department announced that Murtha would face no charges himself.

Granted, that was almost 30 years ago. Certainly, it’s possible that Murtha learned his lesson.

Murtha’s current headache is an FBI investigation into The PMA Group, a defunct lobbying behemoth headed by a former Appropriations Committee staffer named Paul Magliocchetti — “Mags,” as his wine locker at the Capital Grille restaurant identifies him. In recent months, FBI agents have raided PMA Group offices, carting off boxes of evidence.

Given that PMA was ranked last year as one of the largest lobbying firms in Washington, and given its track record in both political giving and in getting earmarks, the FBI’s decision to investigate is not to be taken lightly.

If the investigation is going after any members of Congress, it will not be enough merely to prove the existence of a campaign contribution from a lobbying firm client, or even from a lobbyist, that took place right around the time of a given legislative action.