Teamsters union President Jackie Presser may have been a tipster in the federal investigation that led to the conviction of his longtime union rival Roy Lee Williams, according to sources.

Several sources familiar with the Williams case say that Presser may have provided the Federal Bureau of Investigation with an account of a crucial episode in the investigation: a meeting on Jan. 10, 1979, between Williams and then-Sen. Howard W. Cannon (D-Nev.) in Cannon's Las Vegas office.

Williams and several other men were convicted in December 1982 of having conspired to bribe Cannon as a result of that meeting. Presser was elected Teamsters president in April 1983 in the wake of Williams' ouster.

Reports have persisted over the years, accompanied by denials from the Presser camp, that Presser was a government informer, first for the Internal Revenue Service and then for the FBI, as he climbed in the Teamster ranks.

Speculation mushroomed last week when the Justice Department decided to reject recommendations from its Cleveland office that Presser be indicted for allegedly embezzling funds from Teamsters Local 507, his home base in Cleveland.

Justice Department officials are said to be investigating claims that FBI agents authorized Presser to pay "ghost employes" from his local union's treasury in order to ingratiate himself with mobsters in the Cleveland area.

Williams, undergoing medical examination in connection with a provisional 55-year prison sentence, was, like Presser, an international vice president of the Teamsters union at the time of his 1979 meeting with Cannon. The president was Frank Fitzsimmons, who died in 1981. Fitzsimmons was to have attended the Jan. 10 meeting with Cannon, but according to trial testimony, sent Williams in his place at the last minute.

Williams was subsequently convicted in a federal trial in Chicago of guaranteeing Cannon exclusive rights to buy "Wonderworld," a residential property in Las Vegas owned by the Teamsters' Central States Pension Fund, in return for Cannon's help in squelching trucking-deregulation legislation.

In its prosecution of Williams, however, the government made no mention of a secret informer's report that evidently concerned the Jan. 10 meeting.

The Justice Department instead built its case largely on information overheard in court-ordered electronic surveillance of the telephones and offices of millionaire Chicago insurance executive Allen Dorfman. Dorfman, convicted with Williams and murdered a few weeks later, had been a middleman between Mafia figures and the Teamsters' Chicago-based Central States Pension Fund for years. He arranged the Jan. 10 meeting with Cannon.

The Dorfman surveillance began 20 days after the Jan. 10 meeting as part of a separate investigation of money skimming from Las Vegas casinos and was justified to the federal judge who authorized the surveillance solely on the basis of the skimming allegations.

Defense attorneys, however, say that related court proceedings following the criminal trial turned up evidence of a top-secret "Washington source" for the FBI in the Williams-Cannon case.

"At the time, I thought it was Fitzsimmons," said Washington attorney William G. Hundley, who represented one of Williams' co-defendants. "Now it looks as if I might have been wrong."

Presser was reportedly enlisted as an FBI informer in the 1970s after doing similar work for the IRS. In 1981, however, Labor Department investigators began digging into Presser's activities in Cleveland, including reports of payroll padding at Local 507.

Two other men, including Presser's uncle, have been convicted of taking "no-show checks," but Justice officials this month dropped the case against Presser for lack of "prosecutive merit."

The two agents said to have dealt with Presser in Cleveland could not be reached for comment. But one, Pat Foran, said through an FBI spokesman in Washington that he would have no comment on reports that he had authorized Presser to make the no-show payments.

Foran moved to Washington in 1979 where, one source acknowledged, he might have continued dealing with Presser.

Litigation in Chicago, meanwhile, turned up the existence of a still-secret document that Hundley said was established at a court hearing in March to have been captioned "Sen. Cannon" and to have been dated "pretty close to the Jan. 10 meeting."

Hundley said he concluded at the time that "this was a top-secret Washington report of Williams' meeting with Cannon Jan. 10. I had only one thing wrong. I said it was Fitz . . . . Why would the government still be so secretive about it? After all, Fitz is dead."