Teamsters union President Roy Williams made an unequivocal "commitment" to Sen. Howard W. Cannon (D-Nev.) to deliver a piece of Las Vegas real estate that Cannon and other homeowners wanted to buy, according to a tape recording played in federal court here today.

A voice on the tape says: "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.' " The words were those of Allen Dorfman, a Chicago insurance executive and longtime Teamster associate who is standing trial with Williams and three other men on charges of conspiring to bribe Cannon in return for his help in squelching legislation to deregulate the trucking industry. Cannon has not been charged.

According to the government, the alleged deal eventually fell through at both ends. The independent managers of the assets of the Teamsters' Central States Pension Fund, which owned the Las Vegas property, kept frustrating efforts by Cannon's group to buy the land in 1979. And Cannon, after wresting control of the deregulation issue from Sen. Edward M. Kennedy (D-Mass.), eventually sponsored the deregulation measure that Congress enacted in 1980 over Teamsters' opposition.

In the meantime, however, the FBI had started wiretapping telephones and bugging the offices of Dorfman's insurance agency in the Central States Pension Fund headquarters in northwest Chicago. According to court records, the inquiry was initially fueled by suspicions that Dorfman was controlled by Chicago gangsters and served as one of their front men in gaining control of various gambling casinos in Las Vegas.

But as soon as the wiretap began, on Jan. 30, 1979, the FBI began coming across references to "the senator" and his interest in fending off high-rise development of a 5.8-acre tract of land near his home that the pension fund's new asset managers wanted to sell.

Cannon, chairman of the Senate Commerce Committee at the time, met with Williams, then a Teamsters vice president and a former pension fund trustee, along with Dorfman and a Teamsters lawyer from Washington on Jan. 10, 1979, in the senator's Las Vegas offices.

The main topic, according to Cannon's grand jury testimony previously made public, was the Teamsters' strong opposition to deregulation of the trucking industry, but according to the government's evidence, the interest of the senator and some of his neighbors in the vacant real estate also came up.

The tape recording played in court today reflected Dorfman's earthy exasperation, some four months later, on May 21, 1979, at the Teamsters' failure to deliver the property.

The conversation took place in Dorfman's offices and included Dorfman; a top aide to Dorfman, William Webbe, and a Chicago Teamsters official who had stopped by.

At one point, Dorfman said he had expressed his chagrin to "Roy" just the other day and emphasized to the Teamsters chief that "we made a firm commitment to this guy," a reference to the senator. Dorfman said he had also conveyed his annoyance a few days earlier to Frank Fitzsimmons, then Teamsters president.

Dorfman, whose insurance agency still handles Central States' health claims, said he told Fitzsimmons: "F--- you and your commitments, pal . . . . You don't make commitments to United States senators and then don't fulfill them."

According to the tape, Dorfman said Fitzsimmons replied: "Well, I don't understand why it wasn't fulfilled." At that, Dorfman said he shot back, "Well, I ain't the f------ boss of the International Brotherhood of Teamsters, you are. You ain't figured it out?"

Dorfman blamed the pension fund's assets managers, Victor Palmieri & Co. Inc., for repeatedly frustrating the proposed $1.4 million sale to Cannon's group, and repeatedly referred to the company in obscene language.

Dorfman suggested that Williams should at least have told Cannon that the Teamsters hierarchy didn't really control the pension fund's assets anymore. Instead, Dorfman said, Williams got "a commitment" from Cannon and gave him a firm commitment in return.

Webbe, who said he was in an outer office while Cannon met with Williams and Dorfman in January, 1979, in Las Vegas, agreed with Dorfman's statement that commitments had been exchanged.

Dorfman indicated on the tape that on the way out of the meeting Cannon said: "You fellows will take care of that property thing?" and Williams reportedly replied, "Don't worry, it's all taken care of."

Webbe agreed, stating that "Roy said, 'You take care of your end and we'll take care of our end for you.' "

Questioned by Dorfman's lawyer, Webbe said that he, Dorfman and their guest, Don Peters, had been drinking during the late-afternoon conversation some four months later, in May, 1979. Webbe maintained that Dorfman was simply "upset and spouting" and "I just agreed or added to it."

As for the word "commitment," Webbe insisted that all he understood that to mean was giving Cannon's group "a fair chance to bid" on the Teamsters property.