Mayor Marion Barry, rejecting a request by the D.C. police officers union, said last night that he will not order an investigation of the city police department's controversial drug-testing program.

Union officials told Barry last week that police officials had deliberately concealed key findings of a recent internal probe of the drug-testing program, in which favoritism and other improprieties were alleged. They asked Barry to initiate an independent investigation and demanded that Police Chief Maurice T. Turner Jr. disclose all records from the internal probe.

However, Barry said last night that he was satisfied with the conduct of the three-member police panel that investigated the program. "I'm convinced that there was a thorough investigation," Barry said while appearing on WHHM-TV's "Evening Exchange" program. "There was no cover-up."

Gary Hankins, chairman of the Fraternal Order of Police, declined to comment on Barry's remarks. Hankins said last night that union officials will meet this week with Barry about their request for a new investigation. "We want to wait and see what the mayor has to say in the meeting," Hankins said.

On Jan. 15, Turner announced that the police panel had rejected allegations by two drug-screening employees. The employees had alleged that test results had been manipulated to allow a lieutenant to be promoted after he failed his first test.

But Turner reprimanded two police officials, Assistant Chief Carl Profater and Deputy Chief Jimmy Wilson, for "errant judgment," and said they gave false information to the panel. He also reprimanded Capt. Robert J. Noyes, a former drug-screening official, for violating department rules governing the anonymity of the tests.

Last week, union officials called Turner's disciplinary actions inadequate. They contended that a 17-page summary of the investigation had been "severely edited" to hide evidence of further misconduct. The union said tougher disciplinary action was warranted and, in a 75-to-0 vote, asked Barry to investigate.

After the vote, Hankins said Turner and the panel made a "calculated effort" to obscure the reprimanded officers' improper actions.