Steven Seagal (search) has brought a real-life enemy to his knees - a former movie producer has 'fessed up to using mob muscle to try to squeeze millions from the martial-arts star.

Julius Nasso (search) pleaded guilty to extortion charges for teaming up with the Gambinos in a plot to strong-arm Seagal out of $150,000 per flick after their business relationship soured, Assistant U.S. Attorney Andrew Genser revealed in court yesterday.

The Staten Island film producer is expected to serve one year behind bars under a tentative deal with federal prosecutors, sources said.

His brother Vincent Nasso (search), a pharmaceutical-company owner and alleged Gambino associate, is also set to cop a plea to wire fraud for ripping off a waterfront union medical plan.

He likely faces two years in prison under his plea agreement.

The feds nabbed the Nassos last year as part of a massive roundup that also netted Gambino boss Peter Gotti (search) and powerful mob capo Anthony "Sonny" Ciccone, who were convicted of racketeering earlier this year.

Seagal took the stand in that case as a star witness against Ciccone, who allegedly helped Nasso in his plot to try and squeeze the actor for $3 million after their moviemaking partnership dissolved in the 1990s.

The gun-toting black belt said he had an "uncomfortable" meeting at Brooklyn's Gage & Tollner restaurant in January 2001, where he told Nasso and Ciccone he would try and "work with them."

After the meeting, Nasso allegedly said, "If you had had the wrong answers and things would have gone the wrong way, I think they were going to kill you."

Lawyers for the Nassos, who were set to go on trial next month, have repeatedly branded Seagal a "pathological liar."

"On behalf of Mr. Seagal, this announcement [of the plea deal is] a total vindication of what he testified to at the previous trial," Seagal lawyer Martin Pollner said.

"He's pleased that justice is being pursued and that his name is now clear."

The guilty plea is pending final approval by U.S. Attorney Roslynn Mauskopf's office.