Hollywood action hero Steven Seagal was just trying to weasel out of a $500,000 debt when he allegedly accused a reputed Gambino capo of intimidating him, a defense lawyer charged yesterday.

"If Steven Seagal comes here and testifies there was a threat . . . I'm going to suggest to you that he's a pathological liar," George Santangelo told jurors in Brooklyn federal court.

"He has a reputation all over Hollywood as a liar."

Prosecutors plan to call Seagal, star of such action films as Under Siege and Exit Wounds, as a reluctant witness in the case against Peter Gotti, the brother of John Gotti, and other alleged members of the Gambino family -- who are accused of loansharking and racketeering.

Seagal, the alleged victim, has never publicly spoken about the case and had to be subpoenaed to testify, prosecutors say.

The feds say reputed capo Anthony "Sonny" Ciccone teamed up with Seagal's former producer, Julius Nasso, to squeeze the martial-arts master for millions of dollars.

A crew of mobsters headed by Ciccone allegedly tracked Seagal from New York to Toronto and Hollywood -- threatening to kill him if he didn't shell out $150,000 per movie.

Prosecutors expect Seagal will back up the story.

But Santangelo told jurors: "Every time [Seagal] owes someone money, he cried intimidation. It doesn't happen only here. It happens in other countries."

Seagal's lawyer Martin Pollner declined comment.

Later yesterday, Judge Frederic Block dealt a serious blow to the feds when he barred an FBI agent from identifying subjects in surveillance photos by their alleged mob ranks.

The decision sent prosecutors scrambling for a new way to prove the seven defendants are connected to organized crime.

FBI agent Greg Hagarty had already taken the stand and was expected to identify figures in a massive amount of surveillance photos by their mob rank, such as capo or soldier.

But Block, siding with the defense, said Hagarty could only identify the subjects by their name.

When Assistant U.S. Attorney Andrew Genser protested that he couldn't use the videos and photos unless the FBI agent made the necessary identification, Block told him to try to elicit the information through other witnesses.