A partial human skeleton found last July in a blackberry patch in rural Virginia west of Richmond has been identified as that of an Arlington woman who disappeared in May 1980 on the way to her job as a chemist at Quantico Marine Base.

The death of Bilmaris Rivera, 21, identified through dental records from her home town of Bayamon, Puerto Rico, has been ruled a murder by strangulation, according to M.F. Fierro, Virginia deputy chief medical examiner. Rivera was strangled with a 26-inch shoestring, which was found around the neck of the skeleton, Fierro said.

Rivera, a studious woman who had worked for seven months at Quantico and who wanted to be admitted to Georgetown University medical school, vanished on May 24, 1980, after leaving her Arlington apartment in her green 1974 Ford Pinto. Twenty-three hours later, a Maryland state policeman found the car, ablaze on a deserted road near Frederick.

"We believe she never made it to her job," said Lt. Leslie Parrish, an investigator with the Goochland County Sheriff's Department, which is investigating the slaying along with Virginia and Maryland state police.

Parrish said yesterday that authorities assume that Rivera was abducted on her way to work and taken to Goochland County, about 30 miles west of Richmond, where she was slain. He said Rivera's car was then driven to Maryland where it was set afire.

"If I were going to kill somebody, I would not want to ride a dead person around in my car," Parrish said. "We are working on some leads. We have made no arrests and there have been no interviews of suspects since the body was identified Jan. 21."

Blackberry pickers found the skeleton July 16 last year near the settlement of Oilville. It had been picked over by animals, Parrish said, and bones were scattered over a 30-foot area. Found nearby were a pair of blue jeans and the red T-shirt that Rivera reportedly was wearing when she disappeared.