Charles W. Curtis, charged with murder in the August 1985 slaying of Judith L. DeMaria, who was last seen jogging on a bicycle path near Sterling, admitted to the slaying before his arrest on Thursday, according to records at Loudoun County General District Court.

The arrest was made "after the suspect admitted to murdering DeMaria," the records said. They also indicated that the weapon used was a razor knife, the type used for cutting carpets.

Curtis, a 28-year-old drifter from Martinsburg, W.Va., who has a string of criminal convictions in Loudoun and Fairfax counties, was arrested a few hours after authorities found the remains of a badly decomposed body in a shallow grave about a mile from the spot on the Washington & Old Dominion bike path where DeMaria was last seen.

The remains were taken to the Northern Virginia medical examiner's office in Fairfax to determine the identity of the victim and cause of death.

"There's not much left," Lt. Greg Stocks, spokesman for the Loudoun County Sheriff's Department, said Thursday. "All you're really dealing with is bones and bone fragments."

Although officials were initially unable to determine the sex of the victim, sources at the scene said a bra was found at the gravesite.

Results of the autopsy were expected as early as today.

It is not known whether Curtis, who lived in Northern Virginia off and on during the last several years, knew DeMaria, a 27-year-old tennis instructor at the Capitol Courts Racquet & Fitness Club in Sterling. DeMaria's family told reporters they did not know Curtis, who is being held without bond in the Loudoun County Adult Detention Center in Leesburg.

Authorities said that Curtis, who most recently had been living in his car, contacted Capt. John Sealock of the Loudoun Sheriff's Department on Wednesday, and began giving information that led to his arrest on a murder charge. Sealock, a 14-year veteran of the department, knew Curtis from years ago, when the deputy had arrested him in an unrelated case, authorities said.

Sources said that Sealock had apparently gained Curtis' respect in their earlier dealings. Sealock refused to comment on the case yesterday.

Loudoun authorities declined again yesterday to give specifics about what Curtis told them or what prompted him to come forward. However, "keeping the case in the public eye through the media" played a role, Stocks said, citing reports in the media last month, the second anniversary of DeMaria's disappearance.

Investigators said on Thursday that Curtis' name had come up in connection with their probe, but that someone else had been the chief suspect.

Curtis has a history of criminal convictions. In June 1978, a Loudoun Circuit Court judge sentenced him to four years in jail for three counts of breaking and entering and three counts of grand larceny. The same year, Curtis was convicted of robbing a 7-Eleven store in the county, but he did not serve time on that charge.

Curtis was paroled in May 1979, according to documents in Loudoun Circuit Court. He was later found to have violated the terms of his parole, but action was deferred pending the outcome of a separate court case in Fairfax County.

In June 1980, a Fairfax judge sentenced Curtis to two years in prison for breaking and entering. He was scheduled to be released in March 1983.