A Fairfax County jail inmate, who was awaiting trial on burglary and grand larceny charges, escaped early yesterday while in the custody of a Fairfax police officer at the Trailways bus station in the District, police said.

The police officer, whose name was not released, had signed Timothy W. Parker out of the Fairfax Adult Detention Center Tuesday night to help in several investigations, according to police. The two stopped at several locations in the county before going to the bus station where Parker was to identify another suspect for the officer.

Police spokesman Bill Coulter said Parker went into the bathroom about 2 a.m. and "the investigator never saw him again." Parker was not wearing handcuffs at the station because the investigator and the inmate were undercover, he said.

Using inmates to assist investigators is "not uncommon," said police spokesman Warren Carmichael. However, he added, going to the District under such circumstances was "unusual," and the police department is investigating the incident.

According to a county jail source, the police officer, a seven-year member of the department, was warned by jail officials that Parker was an escape risk and was due in court yesterday. The source said the officer was reluctant to handcuff the inmate, but after some urging handcuffed Parker in front of his body. The more common practice is to handcuff inmates behind their backs, the source said.

Fairfax Commonwealth's Attorney Robert F. Horan Jr. said Parker has at least one previous escape on his record. Carmichael said the department would not comment because the incident is under investigation.

Parker, 27, was serving two five-year concurrent sentences in Missouri on charges of burglary and stealing, said a spokesman at the Department of Corrections in Jefferson City. He said Parker was turned over to Fairfax officials last month to stand trial on the county charges.

Meanwhile, Fairfax and D.C. police officers, including members of the elite Repeat Offenders Project, were searching for Parker yesterday.