The U.S. Immigration and Naturalization Service began an investigation yesterday into reports that a government informant was murdered after the government inadvertently disclosed his identity in court.

Verne Jervis, spokesman for the agency, said the Baltimore INS office is in the process of obtaining from an immigration office in Falls Church the court document that may have disclosed the identity of Lester Domonique, 17, who was beaten and disemboweled near his Hyattsville home Jan. 18.

The Washington Post reported on Sunday that an internal immigration service memo that Domonique may have been slain by Washington area members of the Rastafarian sect, a Jamaica-based religious cult, in retaliation for information that Domonique gave the INS that resulted in deportations.

Jervis said yesterday the INS is taking the position that Domonique's name and phone number were blocked out before the document was admitted into evidence at a deportation hearing in court.

Sources close to the investigation said yesterday Domonique's phone number did appear on the document, although his name may have been blacked out when the document was made part of the court record.

The memo, quoted by The Post on Sunday, was dated Jan. 21 and was titled, "Homicide of an INS Informant." In it, a federal immigration officer said, "It is felt by this officer that [Domonique] was murdered due to possible retaliation to [this] information which resulted in a total of four arrests . . ."

Prince George's County police said yesterday they are continuing to investigate Domonique's death as a routine homicide and that the INS had not contacted them with any new information to indicate the slaying was done in retaliation. County police arrested two suspects in the slaying last week and say they are seeking a third.