NEW YORK (AP) _ The speaker of the New York state Assembly and his top aide cheated their law clients out of thousands of dollars in shady real-estate deals, a prosecutor said Tuesday at the beginning of a federal fraud trial.

But Speaker Mel Miller's lawyer argued prosecutors targeted Miller because of his high political profile and then went looking for a crime and the evidence to back it.

''When you go fishing you want a big fish,'' defense lawyer Gerald B. Lefcourt said of the prosecutors. ''Their eyes were always on the prize.''

According to the government, Miller and Jay Adolf, his chief legislative assistant and former law partner, cheated their clients out of $300,000 in a series of real-estate scams during the mid-1980s.

''Their clients had no idea the defendants had taken and pocketed hundreds of thousands of dollars,'' Assistant U.S. Attorney Matthew Fishbein told the jury.

Miller and Adolf were charged last December in a 19-count indictment accusing them of mail fraud, conspiracy and falsifying documents. The charges involve their now-defunct firm, Adolf & Miller, and not their political activities.

If convicted, Miller faces automatic expulsion from the Legislature and loss of lavish privileges at its helm, and he and Adolf each face up to five years in prison and $250,000 in fines on each count, plus disbarment as lawyers.

Success for the prosecution depends upon whether the jury believes its key witness, Avi Cohen, an admitted conman and income-tax cheat who has been granted immunity from prosecution in exchange for his testimony.

''I think I can guarantee you're not going to like the crimes he admits to,'' Fishbein said of Cohen. ''Avi Cohen's criminal history is not in dispute.''

But Fishbein said Cohen's word at trial was to be believed and that legal documents would corroborate his testimony.

Lefcourt warned the jurors against trusting what Cohen tells them: ''The government has asked you to destroy the lives of respected people based on the lies of this crook,'' he said.

''The government's blind lust for a big political fish gets them to accept it,'' Lefcourt said of Cohen's story. ''The government never carefully looked at Avi Cohen because they were shopping for evidence.''

According to prosecutors, Miller and Adolf joined Cohen in real-estate deals in which Cohen forged documents, lied to the defendants' law clients and kept valuable apartments hidden from real-estate investors who had retained Adolf & Miller.

Adolf's lawyer, Victor J. Rocco, said of Cohen: ''He's lying because he doesn't want to go to jail. He's lying because he doesn't want to face financial ruin and he wants to salvage his empire of greed.''