NEW YORK (AP) _ A judge granted immunity to George Hamilton to compel the actor to testify at Imelda Marcos' fraud trial.

U.S. District Judge John F. Keenan said in his Monday order that prosecutors sought immunity because Hamilton had indicated he would invoke his Fifth Amendment right not to answer questions that might incriminate him.

Hamilton, who has been named as an unindicted co-conspirator in the case, could testify as early as this afternoon. With immunity, he cannot be prosecuted for any wrongdoing but must tell the truth or face perjury charges.

An unindicted co-conspirator is someone who prosecutors claim took some step that advanced a conspiracy but is not charged with a crime.

Hamilton, who played a vampire in the movie comedy ''Love at First Bite,'' is a friend of the former Philippine first lady.

Mrs. Marcos, 60, is accused of helping her late husband, former Philippine President Ferdinand E. Marcos, loot their nation's treasury of more than $220 million to secretly buy four New York buildings and artwork.

Marcos, who also was indicted, died in exile in Hawaii in September. He was ousted as president in a popular revolt in 1986.

Hamilton was mentioned in testimony as having accompanied Mrs. Marcos to view an art collection in New York that the Marcoses allegedly purchased with stolen funds.

Mrs. Marcos is charged with racketeering, racketeering conspiracy, mail fraud and obstruction.

Her co-defendant, Saudi financier Adnan Khashoggi, is charged with fraud and obstruction for allegedly helping the Marcoses hide their ownership of the four buildings and art.

The first witness called to testify today was Carmen Gomez, an accountant who was a long-time employee of Mrs. Marcos' friend, Gliceria Tantoco. Mrs. Tantoco, who owns a department store in Manila, was charged with Mrs. Marcos but is a fugitive.

Mrs. Gomez said that Mrs. Tantoco's son, Bienvenido Tantoco Jr., told her in the spring of 1984 that his mother was in charge of four New York buildings owned by ''F.L.'' She testified that ''F.L.'' stood for ''first lady'' and referred to Mrs. Marcos.