Former Florida congressman Richard Kelly and two codefendants were convicted in U.S. District Court here yesterday of conspiracy and bribery charges stemming from the FBI's controversial Abscam undercover "sting" operation.

The jury's verdict closed out the government's prosecution of six House members -- of which Kelly was the only Republican -- and an assortment of middlemen who were captured on FBI videotape and audio tapes in an elaborate hoax in which agents posed as front men for fictitious Arab sheiks willing to pay for legislative favors. All the congressmen were convicted of federal criminal charges; only one, Rep. Raymond Lederer (D-Pa.), is still in the House.

The seventh and final Abscam criminal case against a member of Congress is pending against Sen. Harrison A. Williams (D-N.J.), who was indicted last October on bribery and conspiracy charges. All of the Abscam convictions face legal challenges, as attorneys for the defendants contend that their clients were lured into the operation and trapped.

Foreman David W. K. Peacock Jr., wearing a yellow ribbon in his jacket lapel in commemoration of the release of the American hostages, delivered the jury's verdict after about 5 1/2 hours of deliberation.

Kelly, 56, a former federal prosecutor and state court judge before he was elected to Congress in 1974, stood expressionless, his hands clasped in front of him as the verdict was announced.

Outside the courthouse, Kelly said he was disappointed but not surprised at the verdict. He said he knew he had to live with the public's perception that all politicians "are a notorious group of liars."

But, he added, "I'm not whining." Asked if he would appeal the verdict, Kelly responded, "The war goes on."

The jury's decision followed a seven-week trial before Chief Judge William B. Bryant during which the government played a videotape that showed Kelly stuffing $25,000 into his pockets during a meeting with an FBI undercover agent at a Washington townhouse in January 1980.

Kelly has maintained that he took the money -- which he returned to the government when the Abscam operation became public -- as part of his own secret investigation into suspicious characters who he thought had infiltrated his congressional office. Kelly, who was soundly defeated in his bid for reelection in the primary last fall, contended that these characters were out to destroy him politically.

A codefendant, New York accountant Stanley Weisz, was shown on tape taking a $50,000 payoff, which he said he regarded as a legal finder's fee for introducing Kelly to the fictitious sheik's representatives. The other codefendant, Robert (Gino) Ciuzio, a Longwood, Fla., businessman, said he took part because he was trying to outwit the sheik's "con men."

Assistant U.S. Attorney Roger M. Adelman called Kelly's defense "a sham" and told the jury that any "honest politician" would have turned aside the bribe immediately. Assistant U.S. Attorney Stephen R. Spivack also represented the government in the case.

Kelly's lawyer, Anthony Battaglia, argued that the government had let "a pack of crooks" loose on Kelly and subjected him to "mind-boggling temptation" to get Kelly to take the bribe. Kelly accepted the $25,000 because he thought it was the only way to get the information he needed for his investigation, Battaglia told the jury.

Commenting after the jury's verdict, Kelly said that he thought that the government during the trial had succeeded in showing that "there were an awful lot of crooks around" who were worth investigating.He said he plans to continue his own investigation and plans to add the government as a target.

Asked by a reporter if he was one of those crooks uncovered during the trial, Kelly responded, "The story of my life has been that I have not been a crook."

Bryant scheduled sentencing for Kelly, Weisz and Ciuzio for Feb. 23. Each faces a maximum of 25 years in jail and more than $40,000 in fines for their convictions of conspiracy and bribery and of a charge of interstate travel in aide of the bribery conspiracy. CAPTION: Picture, Ex-Rep. Richard Kelly . . . pocketed $25,000 on videotape