The jury in the first Abscam bribery trial today heard a tape recording in which an FBI undercover informant urged Sen. Harrison A. Williams Jr. (D-N.J.) to boast of his influence and tell a fictitious Arab sheik that "without me, there is no deal."

On the June 28, 1979, tape, informant Melvin Weinberg, a convicted con man who played a key role in the Abscam undercover investigation, told the senator. "You gotta tell him how important you are, who you are, what you can do, and you tell him in no uncertain terms: 'Without me, there is no deal. I'm the man. I'm the man who's gonna open the doors. I'm the man who's gonna do this and use my influence and I guarantee this.'"

There was a reference in the tape to Williams' receiving some unidentified stock. Sources have said that he received stock in a titanium development company last August, but he has never been charged in the Abscam case.

Weinberg is heard later on the tape telling the senator, "It goes no further. It's all talk. All bullshit . . . it's a walk-through. You should be out of there in 20 minutes . . . you gota just play and blow your horn. The louder you blow and mention names, who you control . . . ."

Defense attorneys introduced the tape in an effort to show that Weinberg set up Williams and, in effect, that Weinberg was an uncontrolled agent who also tried to truck their clients into breaking the law.

Rep. Michael O. (Ozzie) Myers (D-Pa.) and three codefendarts -- Camden, N.J., Mayor Angelo Errichetti and Philadelphia lawyers Howard L. Criden and Louis C. Johanson -- are charged with conspriracy and bribery. Meyers' attorney has acknowledged that the congressman and the others split $50,000 that they received from a representative of the "sheik," who was seeking help with an immigration problem. But the attorney said that the four defendants never intended to break the law.

When the Abscam story broke last February, sources said that Williams had been videotaped several times talking with the undercover agents and had accepted the stock in the titanium development company a year ago.

Justice Department officials have said privately that there are legal problems with the Williams case. For instance, it has been reported that Robert del Tufo, the U.S. attorney for New Jersey, wrote a memo early this year complaining about some of the government's actions in the case. This conduct raised questions about whether the investigation violated the senator's "due process" rights, the memo reportedly said.

At one point on, the June 28, 1979, tape, Weinberg gives the senator instructions about stock: "And when it comes to your shares, you tell him you own 18 percent. You put them in Alex's name. Alex is gonna endorse the back." "Alex" apparently refers to Alex Feinberg, Williams' associate. t

At another point, Weinberg explained that the "sheik" -- actually an undercover FBI agent -- wouldn't say anything of the meeting because "he speaks bad English and he's ashamed of how he speaks."

A voice later identified as that of Williams then asked, "but he understands?"

Weinberg: "He understands perfectly . . . ."

Williams: "What does he know about the properties?"

Weinberg: "He doesn't know anything. . . ."

It is not clear what properties are being referred to, though sources said at the time the Abscam story broke last February that Williams' involvement centered around efforts to develop a titanium mine in Virginia.

George Koelzer, Williams' attorney, said in a telephone interview from New Jersey that he was "not at liberty to discuss the substance" of the tape, which was recorded at a Marriott hotel in suburban Virginia. The attorney repeated his contention that the senator "did not at any time do anything illegal or improper."

Errichetti's attorney, Raymond A. Brown, who introduced the tape today, suggested that Weinberg had tried similar coaching of Myers and his codefendants.

Brown referred, for example, to a tape made on Aug. 15, 1979 -- a week before the alleged videotape payoff to Myers, Brown played a recording of a part of a conversation in which Weinberg and Errichetti discussed the Myers transaction.

Errichetti suggested that he come to New York so Weinberg's "good friend can give me the whole thing so I can understand what's to be done and I can do it." He also referred in that recording to "going over the script."

But Weinberg contended that "we never told them want to say. We told them what we wanted to hear -- what he [Myers] was gonna do for the money."

Brown's cross-examination, which lasted almost the entire day, ended with Weinberg denying that he had received expensive gifts from Errichetti. Brown charged that the informant had accepted a $300 Seiko watch, three Sony 17-inch television sets, a one-ounce gold coin worth $432, a stero, a microwave oven and a Betamax videotape recorder valued at $931.

Each time Brown listed an item that Weinberg supposedly received, he replied, "That is not true."

In their continuing efforts to undermine Weinberg's credibility, the defense attorneys have suggested that he made extra money during the investigation without telling his FBI employers about it.