A purported "bagman" for the Mafia who was found shot to death in Manhattan this month allegedly "socialized on a regular basis" years ago with Labor Secretary Raymond J. Donovan, according to an FBI memo.

The victim of the gangland-style slaying, Fred Furino, 52, disappeared, it was reported yesterday, after repeatedly flunking a polygraph test on a series of questions about whether he knew Donovan.

Furino's corpse, with a bullet hole in the forehead, was discovered June 11 in the trunk of his own car, The Washington Post disclosed last week.

Time magazine reported yesterday that he disappeared after flunking a polygraph test and then being called before a federal grand jury investigating Donovan's alleged ties to organized crime.

"Freddy took a dive six times," Time quoted one investigator as saying of Furino's performance on the polygraph. "Whether Furino also denied any acquaintance with Donovan in his grand jury testimony has not been revealed. But he disappeared from his New Jersey trucking company office shortly afterwards, on June 3."

In another development concerning the Donovan investigation, The Post learned that the FBI deleted from documents made available to the Senate Labor Committee before Donovan's confirmation an allegation that Schiavone Construction Co., where Donovan was executive vice president, was "closely aligned with the Vito Genovese family of the Mafia" through another executive at the company.

The assertion, sources said, came from an informant of the FBI's New York office and was set down in an internal FBI memo dated Jan. 12, 1981, the first day of Donovan's Senate confirmation hearings. The memo evidently was composed by Anthony Adamski Jr., the FBI official in immediate charge of checking out Donovan's qualifications for the Cabinet post.

The document purported to lay out the information that Adamski had furnished the day before, on Jan. 11, in a telephone conversation with White House counsel Fred F. Fielding, who was then the Reagan transition team's conflict of interest counsel.

According to sources, the memo said, in part:

"Two independent sources of the New York Division have advised that SCC Schiavone Construction Co. is 'mobbed up.' One source indicates the upper management of SCC is closely aligned with the Vito Genovese family of the LCN La Cosa Nostra through Schiavone vice president Albert Magrini and its contacts with Jopel Construction headed by William Masselli, who is an alleged self-admitted 'soldier' in the Genovese family." It was not clear, however, just how much the incoming Reagan White House was told.

The memo, which contained several other allegations, including talk of a trip by Masselli and Donovan to Miami for the 1979 Super Bowl, concluded by saying that the "above information" was furnished to Fielding "in general terms to protect the identity of the New York sources."

"Mr. Fielding was asked if he wished Mr. Donovan interviewed concerning these allegations," the FBI memo continues.

"Mr. Fielding stated he did not wish Mr. Donovan interviewed by bureau agents at this time because it would serve no purpose since there were no specific allegations of criminal misconduct."

The memo, sources said, was studded with the initials of at least seven FBI officials.

Although evidently composed by Adamski, it was, on its face, a communication from assistant FBI director Charles Monroe to FBI executive assistant director Francis M. Mullen Jr.

Donovan first testified before the Senate Labor Committee on Jan. 12, 1981, the same day the memo was composed and the day after the Adamski-Fielding telephone conversation.

Donovan testified again on Jan. 27, 1981. So did the FBI's Mullen. He appeared in connection with an FBI report submitted to the committee on Jan. 23, 1981. It omitted all mention of Magrini and the Genovese crime family.

Instead, the report submitted to the Senate committee said: "One source indicated the upper management of Schaivone Construction is closely aligned with organized crime elements through its contacts with Jopel Construction headed by William Masselli, who is an alleged self-admitted 'soldier' in an organized crime group."

Magrini may have been overheard, quite innocuously, on the FBI's extensive wire tapping of Masselli in 1979 when Masselli was a Schiavone subcontractor, but Magrini said he had nothing to say for the moment.

"I've been told by special prosecutor Leon Silverman not to comment until the investigation is over," he said yesterday. "If you want to call me after the investigation is over, fine."

A spokesman for Donovan said Donovan would have no comment. Donovan plans to issue a statement to the press at 2 p.m. today, but the spokesman, Vernon Louviere, emphasized that "this is not an announcement of resignation." He said Donovan would entertain no questions.

Meanwhile, Furino's disappearance and murder are under intensive FBI investigation at Silverman's request under the Federal Obstruction of Justice statute.

According to a memo of one FBI informant who spoke with the bureau on Jan. 27, 1981, the day of Donovan's last Senate hearing:

"Raymond Donovan socialized on a regular basis with Salvatore Briguglio and Briguglio's associates, Paul Cianti, who was also a business agent at IBT International Brotherhood of Teamsters Local 560, and Fred Furino at various nightclubs in the Union City, N.J., area."

That memo remained in the Newark office of the FBI until this spring when it was discovered by Silverman's investigators and then furnished to the Senate committee.

The committee, however, was told by the FBI last year, in an excerpt that was censored from the public record, that Furino, formerly vice president of a mob-dominated Teamsters local in New Jersey, occasionally served as a "bagman" for Briguglio and in that capacity, "picked up money from Ray Donovan" when Briguglio was in jail.

That information was furnished to the FBI on Jan. 21, 1981. Furino, an ex-convict, was interviewed by FBI agents on Jan. 22. He described himself as "one of Sal Briguglio's closest friends" and stated that he was unaware of any payoffs from Donovan or Schiavone Construction.

Furino also offered at the time "to submit to a polygraph in this matter." For reasons that have yet to be explained the FBI did not take advantage of the offer. But Silverman's investigators reportedly took him up on it in late April.