Six Philadelphia police detectives entered a federal prison camp yesterday to begin serving 15-month sentences for civil rights violations in a firebombing case that sent the wrong man to jail.

John Ellis, 43, James Carty, 45, James Crown, 30, James Curley, 50, William Jones, 38, and Roseborough McMillan, 42, entered the minimum security facility just before noon.

At their 1978 trial, the detectives were accused of conspiring to use threats and beatings to obtain statements implicating Robert (Reds) Wilkinson in a firebombing.

Wilkinson went to jail for 15 months after confessing to throwing a gasoline-filled bottle at the home of Radames Santiago on Oct. 5, 1975. The resulting blaze killed Santiago's wife, three children and a young house guest.

But Wilkinson was freed when a judge determined that the man, who is retarded, had signed a confession he was unable to read. He testified that he signed only after detectives stomped him, beat his hands with a blackjack and told him he'd never see his wife and baby again unless he confessed.

David McGinns, a neighbor who laterconfessed to the crime, plea-bargained for a 22-year prison term. An accomplice, Ronald Hanley, was sentenced to life in prison.