It wasn't long after the shrimp cocktail, according to Mario Montuoro, when an executive of Schiavone Construction Co. pulled out an envelope containing $2,000 and handed it to the head of Montuoro's union.

The Schiavone executive did all the talking, Montuoro says. But he also says Raymond J. Donovan, now President Reagan's secretary of labor, was sitting in the next chair when the exchange took place back in the fall of 1977.

Did Donovan, who was executive vice president of Schiavone Construction at the time, know there was $2,000 in cash in the envelope?

"I don't know," says Montuoro who was, at the time, secretary-treasurer of Laborers Local 29 here. "Ask him."

Donovan denied at his confirmation hearings earlier this year that his former company ever made labor union payoffs. He has declined to comment since the FBI began a new investigation on the strength of Montuoro's allegations on this issue. According to one source, Donovan has denied to the FBI that he even attended the luncheon described by Montuoro.

Montuoro says the Schiavone executive--whom he remembers as Joe DiCarlo--enunciated his words quite clearly in handing the envelope to Local 29 president Louis Sanzo.

The senior vice president of Schiavone is Joseph DiCarolis. He could not be reached for comment.

Montuoro says the executive said, " 'Here, Louie, here's a token of appreciation for the help you did for us.' " The bulky Sanzo, Montuoro says, took the plain white packet and stuffed it into a vest pocket of his gray silk suit.

Montuoro, who related these events in an interview with The Washington Post on Wednesday night, says he didn't find out what the "token" amounted to until after the 1977 luncheon at Prudenti's restaurant in Long Island City. He says he attended it at Sanzo's invitation the day before and they drove off together after it was over.

"After we got in the car, Sanzo opened the envelope right away," Montuoro said in the interview. "I was driving. He was counting. They were all one hundred dollar bills. It came to $2,000."

"He gave me $200 and he kept $200 for himself," Montuoro declared. "He Sanzo said, 'The other $1,600, I got to turn it in.' "

"I told the Justice Department I don't know where he turned it in and I don't want to know," Montuoro insists.

Samuel (Big Sam) Cavalieri has been identified in court records as a member of the Luchese family of the Mafia and the real "boss" of Local 29. Montuoro did not implicate Cavalieri in the alleged transaction.

According to Montuoro, who was fired from his union job in 1978 for what he says were his reform efforts, the 1977 luncheon was called primarily to discuss a forthcoming intra-union jurisdictional tussle.

"Sanzo told me the day before, 'Don't make no appointments. We got a luncheon date with the people from Schiavone. It's about a jurisdictional fight with the sandhogs,' " Montuoro recalls.

More precisely, Montuoro says, Schiavone wanted Local 29, a predominantly black union with relatively low wage rates, to keep the better-paid "sandhogs"--Local 147 of the Laborers--from taking over an upcoming subway project in midtown Manhattan.

"It's more expensive to go with Local 147," Montuoro said. For instance, he said, "the sandhogs get showers" and all sorts of other on-the-job amenities. "We get a shanty. We work like animals."

But Schiavone Construction, the former union official adds, didn't want to offend Local 147. The company had used Local 29 on the Vernon Boulevard, a subway project in Long Island City, but it also employed Local 147 on another subway project further out in Queens along Archer Avenue.

"The meeting at Prudenti's was because Schiavone didn't want to take sides," Montuoro said. Instead, he says, the company wanted Local 29 to fight the sandhogs for the work in Manhattan while Schiavone laid back. The jurisdictional squabble, if there was one, would have to be settled by the General Contractors Association, a New York City organization that rules on such matters.

Those who showed up for the lunch besides himself and Sanzo, Montuoro said, were "DiCarlo," company president Ron Schiavone, company project manager Jerry Liguori, and Donovan, the only one Montuoro had never met before.

"Liguori introduced me. He said, 'This is Ray Donovan. He's vice president of the corporation,' " Montuoro said. But as the luncheon proceeded, he said, "I thought DiCarlo was the boss because he was talking all the words. He Donovan didn't say nothing."

According to Montuoro, the "token of appreciation" came first, evidently in connection with the Vernon Boulevard project where Local 29 and its officials were assertedly granted no-show jobs and other favors. Then, he said, "We got into the 63rd Street Manhattan subway b . . . s . . . "

The executive, identified as "DiCarlo" by Montuoro, "didn't want the sandhogs to find out that he wanted us."

Montuoro said he can't say for sure whether Donovan saw the envelope change hands. But Montuoro, who said he was sitting next to Sanzo, says he saw the exchange. "What, am I blind?" he demands.

He also says he heard "DiCarlo" clearly denote it as "a token of appreciation."

"And I'm half-deaf," Montuoro said.

About a week or two later, Montuoro says, he made a presentation on behalf of Local 29 at a contractors association meeting, but by his account, it didn't do much good.

According to a spokesman for the New York transit authority, the Manhattan project, which includes a tunnel under the East River to Queens, is simply divided. Local 29, she said, does the "open cut work" along city streets, and Local 147 does "the underground excavation, electrical and concrete work."

Montuoro said, however, that he believes the sandhogs "got more than us" of the work that he believes ought to be in Local 29's jurisdiction.

A voluble and volatile man, Montuoro has been feuding with Sanzo since his ouster from the union and has campaigned against him for the local's presidency. Montuoro apparently began talking with federal authorities as soon as they contacted him for help in 1978 in connection with an investigation of alleged corruption within the union.

Montuoro says he told federal authorities in the 1978-79 period of the Prudenti's restaurant incident, but he refused in the interview to identify the officials he told.

The allegations, in any case, did not surface during the FBI's investigation of Donovan last winter amid a stream of other charges linking him and Schiavone Construction to organized crime or union corruption or both. The FBI said it could not corroborate any of those claims. Now it has been rushing to complete the new inquiry against a reported Monday deadline. The Justice Department, sources say, has concluded that it must decide by then on whether to seek appointment of a special prosecutor to conduct a full-blown probe under the Ethics in Government Act.

Local 29 president Sanzo, who was convicted earlier this year of income tax evasion and conspiracy charges, was unavailable for comment in the wake of the Montuoro interview. Ronald Schiavone, Joseph DiCarolis and Jerry Liguori also could not be reached.