Lee Harvey Oswald defected to the Soviet Union in 1959, after his discharge from the Marine Corps. Mr. Eddowes, in his book, ''The Oswald Files,'' contended that Oswald never returned and that instead a Soviet spy named Alek James Hiddell assumed the Oswald identity and killed President Kennedy on Nov. 22, 1963. Two days after the President was killed, Oswald was shot in full view of television cameras by a Dallas nightclub owner, Jack Ruby.

Mrs. Porter, her lawyer and a lawyer for Mr. Eddowes were on hand today. According to Mr. Eddowes's lawyer, the coffin contained ''just skeletal remains'' that ''could not be removed in one piece.''

The pathologists here were reported to have taken 150 X-rays. They identified, in the skull, the scar made by surgeons in a mastoid operation when Oswald was 6 years old, in 1945. They said that rings that Mrs. Porter had put on the bodyjust before burial were still there.

After the autopsy, the remains, together with fragments of the wood coffin, were reburied in metal coffin and steel vault. ---- Needs of Family Cited

FORT WORTH, Oct. 4 (UPI) -Marina Oswald Porter has said that she sought to have the remains exhumed for the sake of her family. The 40-year-old Mrs. Porter, who married a carpenter, Kenneth Porter, refused to view the remains but had trusted friends do it. She was asked to identify two rings on Oswald's body.

Mrs. Porter spent hours yesterday in meetings with lawyers in Dallas planning the event. She recalled the years of work leading to it.

''Somehow it hasn't hit me yet,'' she said last night. ''But I just don't know how I'm going to sleep. Kenneth and I have to be up at 4 A.M.''