A D.C. police officer was suspended without pay late Tuesday after officers in an undercover observation post said they saw him involved in an apparent drug purchase in Northwest Washington, police sources said.

Although the alleged seller was arrested and charged with distribution of cocaine, the officer, Curtis Hill, 36, was not charged, the sources said. Charges against the alleged seller were dismissed yesterday by the U.S. attorney's office.

Sources said that officers moved in after seeing an apparent drug deal and seized a quantity of suspected cocaine and a tinfoil packet containing suspected PCP from Hill. However, Hill told the officers he was working undercover and was in the process of arresting the alleged drug seller when they arrived.

Hill's involvement in the incident is being investigated by the department's Internal Affairs Division, sources said.

Hill, a 12-year member of the force who works as a patrol officer in the 3rd District, was off duty when the incident occurred about 7:30 p.m. near 14th and Allison streets NW, according to sources and the arrest book.

The officer was taken to the 4th District station, where he submitted to a breath test and was charged administratively with being intoxicated while off duty, a violation of police regulations, the sources said. They said Hill, whose police powers were revoked, was ordered to report to the Police and Fire Clinic for a physical examination, including a urinalysis.