Bloody clothing was found in the apartment of a man arrested in the shotgun massacre of his estranged wife and six of her relatives at a Michigan farm house, authorities said yesterday.

Pat Hood, a deputy for the Marion County Sheriff's Department, said a pair of blue jeans and a pair of boots, both bloodstained, were found on the floor of an apartment occupied by Robert Haggart, 31.

Haggart, a hog auctioneer, was arrested Thursday night at a roadblock on Hog Jaw Valley Road. Another deputy, Jerry Cagle, said a nickel-plated .38-cal. revolver and two spent cartridge cases were found in the car Haggart was driving.

Those killed in the Tuesday night massacre in Surrey Township in southern Clare County, Mich., were Haggart's estranged wife, Garnetta, 23; her parents, George and Vaudrey Post; another daughter, Helen Gaffney, and three of Gaffney's children. Gaffney's baby, Mandy, was the only survivor.

Haggart is being held on a federal warrant charging unlawful flight to avoid prosecution. He signed extradition papers yesterday that would return him to Michigan to face charges.

Cagle said Haggart took a bus to Michigan last Sunday and returned Wednesday night, driving a 1980 automobile that belonged to one of the victims.

Linda Thomas, 23, who was identified as Haggart's girlfriend and was in the car with him at the time of his arrest, said that when he returned from Michigan he told her the family was "fine."

"I asked him how his family was, and he said, 'Fine.' The Bob I knew, I just can't picture him doing anything like this," Thomas said.