The wife of Melvin Weinberg, a key government witness in the FBI's controversial Abscam political corruption investigation, was found hanged yesterday in a vacant condominium in her Tequesta, Fla., apartment complex, a week after she went on national television and charged her husband with lying at the trials.

Charles McCutcheon, the undersheriff of Palm Beach County, said the death of Cynthia Marie Weinberg, 51, was "an apparent suicide." Local authorities had been searching for her since her 16-year-old son, J.R., reported her missing shortly before midnight Tuesday.

Richard Duke, a Seventh Day Adventist pastor who lived next door, said in a phone interview that he and another man found the body about 4 p.m. in a nearby apartment. He said he found a rose, credit cards and a note by the body that said "she was sorry for what she was going to do, but she just couldn't take the harassment from her husband anymore."

Duke said Mrs. Weinberg apparently tied a rope to the top of the second-floor stairwell in the apartment and then threw herself down the steps. She was found at the bottom of the stairs.

Michael Dennis, a New York attorney who represented one of the Abscam defendants, said he also had represented Mrs. Weinberg in divorce proceedings and was asking the local authorities to investigate the death as a possible homicide.

He was doing so, he said, because Duke had told him she was not suicidal, and in an affidavit she had contended that her husband was threatening her. He also said he had just received from her a packet of material that included checks totaling $1,200 she had written to two FBI agents at her husband's direction.

Justice Department officials said it was possible the checks, which Dennis said were for $900 to Bruce Brady and $300 to Steve Bursey in February, 1980, could have been repayment of loans they had made to Melvin Weinberg.

The investigation, in which undercover agents posed as representatives of an Arab sheik seeking immigration help for bribes, resulted in the conviction of six House members and Sen. Harrison A. Williams Jr. (D-N.J.), despite defense claims the politicians were entrapped by the tricks of Weinberg, a convicted conman turned FBI informant.

Marie Weinberg's accusations that her husband lied about gifts he had taken from targets of the investigation first surfaced 10 days ago in Jack Anderson's syndicated column. Dennis also filed an affidavit in federal court in Washington in which Mrs. Weinberg contended that her husband received color television sets, a Betamax and a microwave oven from some of the men later charged in the cases.

ABC-TV's "20/20" aired details of her charges on Jan. 21.

Weinberg denied under oath during the trials that he had taken any such gifts. Defense attorneys said yesterday they may file motions for new trials or post-conviction hearings on grounds that he perjured himself. The Justice Department also started an investigation of his wife's charges.

"I make this affidavit because I feel my husband committed perjury with the knowledge of the FBI which injured a number of innocent people and I want the truth to be known," she said in the affidavit. "I will be glad to testify under oath in any court as to the truth of the foregoing."

She also said in the affidavit that "my husband was threatening me" because she was talking with Indy Badwhar, an Anderson reporter.

Sgt. Thomas Thompson of the Palm Beach, Fla., County Sheriff's office said yesterday, in an interview shortly before the body was found, that Mrs. Weinberg's car keys and wallet were left in her apartment when she left. There was no sign of a struggle and she was considered a missing person at the time, not the victim of a kidnaping, Thompson said.

A nationwide alert had been issued in an effort to find her, Thompson said. Weinberg was in Thompson's office when a reporter called yesterday and the sergeant said he was "concerned and is cooperating."

An FBI spokesman said the bureau is following the case, but so far has no jurisdiction to enter the search. Federal authorities would welcome evidence to back Dennis' claims about the checks to FBI agents, the spokesman said.

All during the Abscam trials, defense attorneys attempted to shift the juries' attention to Weinberg's unsavory past, rather than the conduct of their clients. Chief Abscam prosecutor Thomas P. Puccio countered that it was the secret videotapes of the congressmen and their own testimony that were the crucial evidence in the cases.

Dennis said he had planned to use Marie Weinberg as a witness in "due process" hearings in Washington charging government misconduct in the case in which his client, Stanley Weisz, was convicted along with former representative Richard Kelly (R-Fla.).

Richard Ben-Veniste, attorney for Howard L. Criden, who was convicted along with expelled reprresentative Michael (Ozzie) Myers (D-Pa.), said was considering a motion for a new trial in Brooklyn because of Weinberg's possible perjury. An attorney for former representative John Jenrette (D-S.C.) said he would file a similar motion.

Ben-Veniste said after hearing of Mrs. Weinberg's death: "This is another tragedy. It's just pitiful how this Abscam has ruined the lives of so many people."