Justice Department prosecutors are planning to introduce testimony in federal court next week alleging that Teamsters union President Roy Lee Williams receives some of the proceeds from skimming operations at Las Vegas casinos from the Kansas City organization of reputed crime boss Nick Civella.

The proposed testimony, outlined in court records here, would come not from the government informer who made the accusation but from an FBI agent in Kansas City who has read secret reports identifying the informer and recounting what he has told the bureau over the years.

The controversial procedure never could have been used at the trial of the Teamsters chief and his confederates, all of whom were convicted in December of attempting to bribe a U.S. senator. Defendants have a constitutional right to confront their accusers.

That right does not extend, however, to the kind of presentencing hearings being held by U.S. District Court Judge Prentice H. Marshall.

Under a procedure first used in Brooklyn in 1978 against two reputed members of the Mafia, it has been held by a federal appellate court that out-of-court declarations by an unidentified informer, where there is good cause for keeping his identify secret and where his information can be corroborated, can be used for sentencing purposes without violating a defendant's right to due process or to confrontation.

To government prosecutors, the approach is sometimes necessary, especially in cases involving organized crime.

Congress decreed in 1970 that "no limitation shall be placed on the information concerning the background, character and conduct" of a defendant which a federal court "may receive and consider for the purpose of imposing an appropriate sentence." And the Supreme Court has held that a broad and largely unlimited inquiry is needed if the punishment is to "fit the offender and not merely the crime."

To defense lawyers, the approach smacks of a medieval inquisition. For the past week, Frank Oliver, the new lawyer for one of Williams' co-defendants, alleged Chicago mobster Joseph Lombardo, has been protesting loudly that the judge would be better advised to use a 500-year-old tract promulgated in 1484 by Pope Innocent VIII for the conduct of heresy trials and containing such helpful bits of advice as "speak rather as an informer" when dealing with witches because of their great powers.

"I think it alarming, 500 years later, that courts should be indulging in this same type of reasoning," Oliver said.

Judge Marshall acidly rejected the notion and said he was satisfied that the four rulings emanating from the Brooklyn case constituted a fair guide. The rulings, the judge observed, represent "the only body of contemporary American law on the subject."

Ruling in a case involving Carmine and Daniel Fatico, two alleged members of the New York Gambino crime family who had been convicted of receiving goods hijacked from Kennedy International Airport, Judge Jack Weinstein decided that the government would have to prove the brothers' membership in organized crime "by clear, unequivocal and convincing evidence" in order to justify a stiff prison term.

The judge noted that the government had produced two government-protected witnesses and seven law enforcement agents who testified that 17 different informers had told them the Faticos "were 'made' members of the Gambino family." Weinstein held that the burden had been met.

In the sessions here, the first so-called "Fatico hearings" to be held in the Chicago-based Seventh Circuit, chief prosecutor Douglas Roller began by producing FBI tape recordings and three government-protected witnesses who linked Lombardo to as many as five murders in the Chicago area.

On Thursday, however, Roller sought to employ the "Fatico" rule and carry it a step farther by calling on FBI agent Peter Wacks to recount the allegations of three informers he had never met.

Wacks had simply read the informers' reports, some as many as 12 years old, about organized-crime activities in Chicago, where the Teamsters Central States pension fund is headquartered, and in Kansas City, which is Teamster President Williams' home. Roller said the informers or their families would be in danger if their names were revealed.

Marshall refused to hear Wacks' testimony. Marshall said such testimony would fall far short of the "clear, unequivocal, convincing evidence" he wanted.

"It is third-level hearsay, gentlemen, at the very best, and by the same token, the very worst," the judge ruled.

Marshall also said that in the original "Fatico" hearing the lawmen who testified had, he believed, all dealt with the informers they were quoting and could be cross-examined as to their opinions of the anonymous sources. He said he felt the defendants were entitled to that much, at least.