A 17-year-old who was released by mistake Tuesday from Fairfax County jail, where he was being held under $50,000 bond in the throat slashings of four persons, was back in custody yesterday after being apprehended at a girl friend's apartment south of Alexandria, police reported.

Meanwhile, police said they had begun a search for another of the suspects charged in the slashings whom they had thought was jailed in the District of Columbia. Investigators said they learned yesterday that the suspect was free under $1,000 bond in an unrelated District case.

The 17-year-old suspect, Phillip A. Boyd of 9925 Corsica St. Vienna, who had been freed from the Fairfax jail because of a clerical error about 4 p.m. Tuesday, was apprehended at 12:20 p.m. yesterday by two Fairfax County officers acting on a tip, police said.

The youth had been certified by the county Juvenile Court to stand trial as an adult and faces four charges each of attempted murder, attempted abduction, armed robbery and use of a firearm during commission of a felony.

Chief Depty Fairfax Sheriff Bud Greenquist said yesterday: "I want to accept partial responsibility for the administrative oversight," that freed Boyd. The sheriff's department runs the jail.

Greenquist said jailers had been unware that there were documents at the jail stating that Boyd should not be released.

Boyd is one of six persons charged in the throat slashings Aug. 28 of two men and two women in an apartment at 9136 Barrick St., Fairfax County.

When Boyd was arrested Sept. 9, he told police he was 18, so he was charged in the county's General District Court, which tries adults in misdemeanor cases and give preliminary consideration to felony (more serious) cases.

When it was later determined that Boyd was only 17, his case was transferred to Juvenile Court, which certified him for trial as an adult at the request of the county prosecutor, and referred the case to the grand jury. At this point Boyd was in the jurisdiction of yet a third court - Circuit Court - which tries adult felony cases.

The original charges against Boyd were dropped Tuesday by the General District Court and the youth was promptly freed by his jailers.

Chief Juvenile Court Judge philip N. Brophy said yesterday that "three were cards (ordering Boyd held) in the sherrif's office."

While acknowledging this, Greenquist said that the various shifts from court to court had produced 40 prosecution slips on Boyd, and the jailers were unaware that among them were ones ordering the youth held.

The suspect, who police said they learned yesterday was free instead of being jailed in the District, is John Alfred Austin, 24, of 1408 Allison St. NW.

A spokeman for D.C. police said that when Fairfax police notified them Tuesday that Austin was being sought in connection with the throat slashings, a computer reported that the suspect was being held in D.C. jail on an unrelated charge.

When warrants were sent to the jail ordering his detention in connection with the Fairfax charges, police said, it was discovered that he had been freed under $1,000 bond last Friday after being jailed for two days in connection with a robbery.

Of the six suspects charged by Fiarfax police in the slashing incident, three are now jailed in Fairfax, one is in custody in South Carolina. While Austin and a sixth man, who has not been publicly identified, are still being sought.