The U.S. Immigration and Naturalization Service acknowledged yesterday that an informant's home telephone number was improperly disclosed at a deportation hearing in November. Two months after that hearing the informant, 17-year-old Lester Domonique, was slain.

Verne Jervis, spokesman for the INS, said the agency is still trying to determine whether the disclosure of Domonique's telephone number led to his killing. Domonique was beaten and stabbed to death outside his apartment in Hyattsville Jan. 18. His death was called a retaliation killing in an internal INS memo obtained by The Washington Post last month.

Prince George's County police have arrested three suspects on murder charges in the slaying and said yesterday their investigation is complete.

Domonique's name, but not his telephone number, was blacked out on a document admitted into evidence at the deportation hearing, Jervis said.

Jervis noted that informant report forms, are rarely introduced at deportation hearings. But he said general policy is to black out any information that might identify informants.

"The number was not crossed out," he said. "We are now trying to determine whose repsonibility it was" to black out that information on the document in question.

Jervis said his agency's investigation -- conducted by its Washington-based Office of Professional Responsibility -- has been broadened to include a review of all procedures involving informants. "We don't want this to happen again," he said.

The internal INS memo obtained by The Washington Post said that both Domonique's name and phone number were revealed in the document. Jervis said yesterday that Domonique's name was not disclosed.

The memo, dated Jan. 21, was written by a federal immigration officer and said, "It is felt by this officer that [Domonique] was murdered due to possible retaliation to [his] information which resulted in a total of four arrests. . . ."

It also said that "although every attempt was made to safeguard the informant's identity, the admission into evidence of the original [informant's report form] . . . and [Domonique's] continued association with [a group he was informing on] did ultimately lead to his murder."

According to the INS, the persons on whom Domonique was informing were members of the West Indian Rastafarian sect.

Prince George's police said yesterday Domonique's death was investigated as a "routine homicide" since the INS had not informed police initially that Domonique was an informant. The three suspects in the killing are two adults and a juvenile.

Jervis confirmed yesterday that the author of the memo has been reassigned to different duties.

Jervis said the action was not taken to punish the officer for writing the memo but resulted from a general office policy. The INS has decided to take all similar officers off investigative duties, he said, and that includes several others besides the memo's author.