The Senate Labor Committee's chairman and ranking Democrat have demanded that the Justice Department respond to a series of unanswered questions about alleged Mafia connections with Secretary of Labor Raymond J. Donovan's former construction company.

The demand was made after a secret Justice Department briefing late Friday afternoon for committee Chairman Orrin G. Hatch (R-Utah) and ranking minority member Edward M. Kennedy (D-Mass.). Donovan is currently under a new FBI investigation because of allegations he was present at a 1977 payoff of a New York labor union leader by another executive of Donovan's company, Schiavone Construction.

The questions were first posed last July by Hatch and Kennedy. The FBI refused to answer them then because of "protective court orders" covering the bureau's secret wiretaps and electronic eavesdropping in 1979 at a South Bronx warehouse run by William P. Masselli, a suspected member of a New York Mafia family.

A trucking company Masselli headed had grown into a multimillion-dollar-a-year business subcontracting on New York City subway projects for Schiavone Construction.

At least one conversation the FBI picked up dealt with invitations to Masselli to fly to a function with "Ronnie Schiavone and Ray Donovan."

Donovan denied any social or personal relationship with Masselli in sworn testimony at Senate confirmation hearings last January. There had been allegations at the time that Schiavone Construction, of which Donovan had been executive vice president, was "mobbed up," largely because of contacts with Masselli.

The FBI, however, testified that it had not been able to corroborate any of the claims. It made no mention of the tape-recorded references to Donovan and Ronnie Schiavone until this past summer, after Hatch and Kennedy learned through press reports of the eavesdropping.

The bureau then disclosed there had been a brief conversation between Masselli and his son, Nat, about an invitation Masselli had gotten from some unnamed individual to hitch a plane ride with "Ronnie Schiavone and Ray Donovan" to some affair for which the friend had tickets.

The FBI report last July offered virtually no other details, nor did it mention whether there had been any other references on the hundreds of Masselli tape recordings to Schiavone officials.

At the Friday briefing, according to informed sources, Justice Department officials acknowledged that the ostensible reason for the secrecy last summer--the investigation of Masselli--is no longer valid. Masselli pleaded guilty this fall to reduced charges involving a hijacking ring and a conspiracy to manufacture more than $100 million worth of synthetic cocaine. He was sentenced last month to seven years in federal prison.

The tapes, however, were resealed by federal court order on Nov. 23. Thus far there is no indication on the public record of renewed interest in them by federal authorities or anyone else.

The Friday briefing also dealt with the new FBI investigation into allegations of a $2,000 payoff of a New York labor leader in Donovan's presence. Senate sources said Hatch and Kennedy were told that the provisions of federal law aimed at determining whether a special prosecutor should be appointed required complete secrecy.

Sources said Hatch and Kennedy responded with a letter asking for a copy of the Justice Department's report as soon as it is made to the U.S. Court of Appeals here.