Rep. Raymond Lederer (D-Pa.) was absent today from a federal courtroom as his trial got under way on charges stemming from the FBI'S Abscam investigation. He was in Washington , being sworn in to the new Congress.

Lederer is the only congressman reelected after being charged in the Abscam political corruption investigation.

Lederer, 42, of Philadelphia, is charged with bribery and conspiracy. He is the sixth congressman to be tried in the Fbi's two-year investigation.

Lederer waived his right to be present for jury selection. A anel of nine men and three women was selected to hear his case.

Judge George Pratt granted a motion by defense lawyers to sever three other defendants -- Camden, N.J., Mayor Angelo Errichetti, Philadelphia, lawyer Howard Criden and Philadelphia City Councilman Louis Johanson -- from his trial.

A federal grand jury indicted him May 28 on charges of accepting a $50,000 bribe from an undercover FBI agent in return for a promise to help a ficititious Arab sheik remain in the United States.

The meeting was videotaped and will be replayed during the trial.

Lederer is also accused of splitting the payoff, made during a September 1979 meeting at a hotel near Kennedy Airport with Errichetti, Criden and Johnson.

The Abscam trial of Rep. Richard Kelly (R-Fla.) resumed in federal court today with testimony from a former Kelly aide once suspected of cocaine trafficking.

Questioned in court, with the jury absent, J.P. Maher refused to confirm most details of an affidavit he signed in 1977 concerning his activities in Bolivia.

Sections of the affidavit read in court by Kelly's attorney, Anthony Battaglia, showed that Maher acknowleged in 1977 that he was involved in a cocaine transaction in La Paz. According to the affidavit, Maher was questioned in La Paz by an agent of the U.S. Drug Enforcement Administration.

He said he agreed to cooperate with U.S. investigators "in one incident."

No charges were brought against Maher as a result of the drug incident.

Maher was working as Kelly's Florida district assistant as the time of the cocaine incident.

Kelly has contended that it was Maher who introduced him to the middlemen charged with arranging a bribe of the congressman.

By calling Maher to the stand, Kelly's attorney was trying to establish that the congressman had become suspicious of Maher after the cocaine incident and that when the assistant brought in the middlemen, his suspicions increased.

Kelly's basic defense is that he accepted $25,000 in cash from FBI undercover investigators only as a way of conducting his own probe of what he concidered a shady operation.

Kelly's trial had been recessed for almost two weeks.