A special police panel is investigating whether police officials, including members of the department's Internal Affairs Division, tampered with drug testing procedures in at least one case where a high-ranking officer's urine tested positive for drugs, D.C. police officials confirmed yesterday.

Officials of the police union in confidential letters sent late last month to Mayor Marion Barry and U.S. Attorney Joseph E. diGenova asked them to examine "allegations of misconduct and possible criminal violations" by D.C. police officials. The potential criminal violations, according to the letters, include bribery, tampering with physical evidence and standards of conduct.

Letters and other documents obtained by The Washington Post show that the allegations center on "irregularities" in the department's drug testing procedures, and may involve other areas of the operation of the Police and Fire Clinic, located at 2 D.C. Village Lane SW.

"If the system has been corrupted, the ramifications are widespread," Robert E. Deso, attorney for the Fraternal Order of Police, wrote in a seven-page, July 16 letter to diGenova detailing the allegations. "If records have been falsified, false statements are made, or testing procedures subverted for gain (such as promotion), it is likely that criminal as well as ethical violations have been committed."

Central to the police probe is a May 30, 1985, drug test of a lieutenant who was in line for promotion to captain but tested positive for marijuana in a prepromotion physical at the clinic.

Later that day, according to the documents, the man returned for a second drug test, which is not usually given and was not conducted in the police laboratory as is the normal procedure. At the direction of an unidentified, high-ranking police official and under the supervision of officials from the Internal Affairs Division, the second sample instead was ordered hand-carried by a police officer on a plane to a lab in North Carolina, according to the documents.

When the second sample was returned from that lab to the clinic, it was reported free of drugs, according to the documents.

The lieutenant received his captain's bars and became commander of the department's narcotics branch and later served on the department's Adverse Action Panel, which decides whether to fire police officers who have tested positive for drugs.

The officer, who now holds another position, was on leave yesterday and could not be reached for comment.

The documents also allege other improprieties at the clinic, including "deliberate falsification of record," and drug screening records missing from locked and confidential clinic files.

Police Chief Maurice T. Turner Jr. and other police officials yesterday confirmed the existence of the investigation but declined to comment on it.

"I have no comment on an ongoing investigation. It would be unfair for me to comment. It's premature," said Turner, who is mentioned in the documents as possibly having ordered the unusual second chance for the lieutenant. "I'm concerned about any allegation of wrongdoing by any police officer."

Spokesmen for diGenova and Barry yesterday acknowledged that the U.S. attorney and the mayor are fully aware of the allegations but declined to comment.

The panel, appointed this month by Turner, is chaired by Ronal D. Cox, assistant chief for inspectional services, and includes Melvin C. High, assistant chief for technical services, and Terrence D. Ryan, an assistant general counsel for the department. Closed-door investigative hearings on the allegations began last week, according to sources, and are continuing.

While the probe centers on the allegations of tampering with the "If the system has been corrupted, the ramifications are widespread."

-- Robert E. Deso

officer's test results, the scope of the investigation goes far beyond it, according to sources.

Drug screening tests figure prominently in recruiting police officers, in promotions and in clearing or convicting officers accused of substance abuse.

"The . . . incident {with the lieutenant} seems to be the most concrete example of going outside of procedures to protect one individual," said a source close to the investigation.

"They're {the panel members} just getting into whether there have been widespread abuses and whether the system is being administered in such a way that it can be manipulated in any way; one way might be to protect officials, another might be to see that someone who is not in good graces -- a problem officer -- comes out dirty," the source said. "Another might be to judge favorably or unfavorably candidates for police officers, promotions, fitness for duty."

Since the department drug screening program began in 1982, about 40 officers have lost their jobs after testing positive for drugs, according to police and union officials. If the investigation substantiates improprieties in the screening, those officers could appeal their firings, sources said.

The alleged compliance of Internal Affairs Division officials in tampering with drug tests, files or documents raises questions because the division is supposed to uncover and investigate misconduct on the part of police or D.C. government officials.

"I do not question in any way the integrity of the three officials who are conducting this investigation," Deso said in an interview yesterday. "I am aware, however, that ultimately the department as an institution has a vested interest in attempting to minimize the significance of any questionable or improper conduct that could compromise its entire drug testing program."