The FBI, after more than four years of controversy, is trying to determine whether there was a bureau cover-up in connection with the organized-crime surveillance that indirectly led to indictment of former U.S. labor secretary Raymond J. Donovan and nine others.

Informed sources said the word "cover-up" was used in recent weeks in questioning several FBI agents associated with the 1979 case, named Operation Tumcon.

The FBI's Office of Professional Responsibility began conducting the internal investigation last fall and, according to one source, the bureau has established an "independent squad" to probe possible crimes uncovered in Tumcon that might be prosecuted.

As far as can be determined, no FBI agent or management official questioned has said he has information concerning a possible cover-up.

The current inquiries appear to have been instigated by developments in Bronx Supreme Court in March, beginning with disclosure of hundreds of previously secret summaries of conversations overheard during Tumcon wiretap surveillance.

The summaries included allegations of crimes ranging from gangland murders to bribery and political corruption involving federal, state and local officials.

Disclosures in court March 6 of some Tumcon conversations produced publicity about the fact that the $1 million FBI inquiry resulted in only two federal indictments.

The internal review of how Tumcon was handled came as a result of the indictment of Donovan and others under New York state law on charges of fraud and grand larceny involving his company, Schiavone Construction Co. of Secaucus, N.J.

Not until late March did the FBI reportedly begin asking agents connected with Tumcon whether they knew of any attempt to "cover up" matters regarding any part of the Tumcon investigation.

The new line of questioning apparently coincided with a Bronx Supreme Court ruling that there was sufficient credible evidence to sustain Donovan's indictment and with Donovan's resignation from the Cabinet the same day.

At the time of Donovan's 1981 Senate confirmation hearings, the FBI's New York office had sent a memo dated Jan. 10, 1981, to FBI headquarters. It was only partially shared with Senate Labor Committee members considering Donovan's nomination.

Made public recently in connection with Donovan's court case, the memo stated that a review of the Tumcon file showed that William P. Masselli, a reputed member of the Genovese organized-crime family, "has a very close and personal relationship" with Schiavone Construction.

That relationship, the memo stated, included "preferential treatment on subcontracting projects, financing of equipment for Masselli to lease back to Schiavone and numerous, possibly fraudulent schemes to raise federally required minority participation levels in urban mass transit projects."

The chief FBI spokesman at the Donovan hearings, former executive assistant director Francis M. (Bud) Mullen Jr., did not mention those assertions. He told the Senate committee Jan. 27, 1981, that FBI background checks on Donovan amounted to "a favorable investigation" for him and Schiavone.

Mullen admitted in mid-1982 that he "consciously" withheld from the Senate the fact that Donovan's name had been mentioned on a wiretap involved in an organized-crime probe. Mullen maintained that the conversation was "not pertinent" to the background check.

The Senate committee's special counsel concluded in 1983 that the FBI had withheld "pertinent" and "significant" information from the panel.

Donovan, Masselli and eight other men face trial on charges of conspiring to defraud the New York City Transit Authority of $7.4 million.

Meanwhile, assistant FBI director in New York Lee F. Laster, 52, is leaving for a job in private industry, and deputy assistant director Kenneth Walton is leaving to head the Detroit office. Both were among FBI personnel questioned recently in the OPR investigation. FBI officials said neither move is connected with the probe.