A former promotion manager for the Beatles has secretly pleaded guilty to income tax evasion and is expected to be a prosecution witness in the trial of Allen Klein, former Beatles' manager.

Klein is scheduled to go on trial today in U.S. District Court in New York on six counts of income tax evasion and filing false tax returns.

Court documents, sealed for six months until their release Sept. 30 also disclose that another important government witness in the trial will be Peter Benedetto known professionally as Pete Bennett.

Bennett worked for Klein in the early 1970s when Klein was managing the British rock group, whose four members no longer perform together.

Bennett and Klein are accused of selling promotional copies of records, which they were supposed to be giving away, then failing to pay taxed on the money they received for the records.

Bennett was indicted Dec. 16 on six counts of tax evasion. Klein was indicted on similar charges April 16.

While a grand jury considered the charges against Klein, Bennett was secretly plea bargaining with federal prosecuters to testify against hif former boss. On March 14 he plead guilty to a single count of filing a tax return.

Bennett's guilty plea and all evidence of his cooperation with the government were ordered sealed by federal Judge Vincent L. Broderick, at the urging of both prosecuters and defense attornies.

The record remained secret until Sept. 30 when Judge Edward Palmieri unsealed the court records. Although the indictments of Bennett and Klein were widely discussed in the music world and were publicized by prosecutors, there was no announcement, when Bennett's guilty plea was unsealed.

Court documents detailing the unusual secrecy were obtained for The Washington Post by John Kennedy, a New York legal research specialist.

The court records indicate Bennett's plea was kept secret to prevent Klein from learning that Bennett would be a witness against him and to protect Bennett from possible danger.

"We have some reason to believe that Mr. Benedetto's (Bennett' family and his personal safety could be placed in jeopard," Bennett's attorney Martin Schwartz, told Judge Broderick in arguing to keep the plea secret.

Schwartz said there were "clear indications of threats against the family of the defendant on the part of some people who were perhaps in the employ of Mr. Klein" or his lawyer, Schwartz said.

He said an unnamed investigator for Klein's attorney was in Bennett's neighborhood in Hartsdale, N.Y. asking questions about Bennett's children, such as "Where were they? Where did they go to school? What time did they come home from school?"

Thomas Engel, the assistnat U.S. Attornye prosecuting the case, told Judge Broderick that Bennett has been promised protection by U.S. Marshalls. He also has been offered the services of the witness protection program in which guards-hiding places and even new identities have been provided ot witness fearful of reprisals.

The charges against Bennett and Klein date back to 1970 and 1971. They involve the sale of Beatles' recoreds and recordings of the Concert for Bangladesh, a Madison Square Garden benefit for victims of the war between India and Pakistan, which resulted in the creation of Bangladesh.

Klein became the Beatles manager in 1969, setting off a dispute within the group that eventually lead the famed musicians to break up, Klein was hired by John Lennon with the consent of Ringo Star and George Harrison. But Paul McCartney refused to accept Klein as manager and eventually sued to dissolve the group.

Klein was president of ABKCO Industries of New York, which shared the address of Apple Records, the Beatles' own label. Bennett was hired to promote records for ABKCO, Apple and later for the Bangladesh concert.

According to the indictments, Klein and Bennett received promotional copies of records which were meant to be given to reviewers, radio stations and others to encourage sales.

Instead they sold the records through wholesalers and distributers. In some cases the two allegedly asked that the usual stamp "Promotional Copy not for sale" be left off the records they got.

Bennett's guilty plea was to a charge that he failed to pay income taxes in 1971 on "payments from wholesalers, distributers and jobbers for the sale of phonograph records intended solely for the promotional use of the Beatles and other performers."

Five related tax evasion charges remain pending against Bennett. Under the [WORD ILLEGIBLE] agreement those changes are to be dismissed at the time he is sentenced, which will be after he has testified against Klein.

Klein's trial is expected to take four to six weeks. Bennett's sentencing is set for Oct. 22.

Bennett's secret plea had to be made public before the Klein trial in order to give defense lawyers the opportunity to prepare to refute his testimony.

Klein's attorneys suspected that Bernnett might be cooperating with prosecutors. Several weeks ago they sought to gain access to the court records but were turned down by Judge Broderick.