A federal prosecutor accused Teamsters President Roy Lee Williams and his co-defendants today of trying to cover up a blatant scheme to bribe a U.S. senator with an "absolutely incredible" pack of lies.

In a forceful final summation, Douglas Roller, head of the Justice Department's Organized Crime Strike Force here, reinfored his plea for a string of guilty verdicts with a hard-hitting replay of eight of the most incriminating conversations underlying the government's case in the two-month-long trial. The records, played in striking succession today, were the result of secret electronic surveillance by the FBI.

With the voices booming out over four powerful loudspeakers in the courtroom, one of the main defendants, Chicago insurance executive Allen Dorfman, could be heard complaining in exasperated tones of the unequivocal way in which he said Williams had promised Sen. Howard W. Cannon (D-Nev.) some Las Vegas real estate.

Dorfman expressed his indignation because the Teamsters had yet to make good on the commitment even though, at a Jan. 10, 1979, meeting in Cannon's Las Vegas office, according to Dorfman, "Roy Williams just unequivocally came right out and says, 'You got the property, senator, don't worry about it. It's our property, you own it.' "

"You know, I, I'm surprised he Cannon still even talks to me," Dorfman told associates in his office on May 21, 1979, after a phone conversation with Cannon about the delay in the property transaction. " . . . I'm going to wear out my welcome with this guy. We keep going to him for favors, he keeps performing, we keep delivering him s---."

The government has charged that Williams, then a Teamsters vice president, and Dorfman, a longtime Teamsters associate, guaranteed Cannon exclusive rights to buy a 5.8-acre tract owned by the Teamsters Central States Pension Fund in return for Cannon's help in squelching trucking deregulation legislation.

Roller charged there were "frantic efforts" to make good on the promise, including a hurried flight to California by a fund trustee and a former trustee to persuade another bidder to drop out.

According to the tapes, reputed Chicago mobster Joseph (Joey the Clown) Lombardo suggested the Jan. 30, 1979, trip and, when it proved successful, claimed credit.

In his closing argument, Lombardo's lawyer, Harry J. Busch, derided the government's description of Lombardo as the "pragmatist" of the conspiracy.

"I don't think Joe Lombardo knows the meaning of the word," Busch told the jurors. He described his client as "an absolute nothing in this deal."

In his closing arguments, Dorfman's chief attorney, Harvey Silets, charged that the government was trying to "flimflam" the jurors by using the tapes to divert their attention from the crucial Jan. 10 meeting in Cannon's office. Silets maintained there was no showing that Williams and Dorfman "cut a deal" with Cannon at the meeting despite all the talk the FBI picked up on the tapes.

Silets also scoffed at the government's contention that a chance to pay $1.4 million, in league with 11 others, for a piece of property valued on the pension fund books at $960,000 could be fairly described as a bribe. The property was eventually sold to another party for $1.6 million. Prosecutor Roller emphasized that "whether that bribe was accepted or not does not matter" since "Sen. Cannon is not on trial."

Silets asked the jurors to consider "if there truly was a deal with Sen. Cannon, why wasn't he indicted?" The prosecution promptly objected, and U.S. District Court Judge Prentice Marshall told the jurors to ignore the remark.