Lt. Col. Thomas M. Davis, the highest ranking black officer on the Prince George's County police force, resigned under pressure yesterday after being accused of asking subordinates to falsify test scores of blacks seeking to join the department.

Chief Michael J. Flaherty said he asked Davis to resign because a recent departmental investigation concluded that two years ago Davis pressured three black officers who are recruiters in the personnel department to add extra points to the scores of black applicants so they would be accepted into the police academy.

Flaherty said the investigation determined that those officers refused to change scores.

"I cannot allow someone at that level to use his or her position to force people to adjust scores or manipulate the process," Flaherty said.

Davis was the chief of the Bureau of Administration, which includes personnel, training and internal affairs. His position was that of a political employe who served at the pleasure of the police chief who could dismiss him at will.

Flaherty also said the complaining officers provided him with a tape recording of a conversation in which Davis is alleged to have asked the recruiters to change scores.

In an interview last night, Davis denied wrongdoing and said he is aware of the existence of a recording, but does not recall making such a request. He also said that the officers who made the complaint against him have long harbored ill feelings toward him because he did not support them in an earlier incident.

"I don't ask anyone to do anything illegally," Davis said. He said he has often told recruiters that "if a person misses a test by a few points and he has two arms and two legs . . . we have a responsibility to help that individual reach his or her goal." He said he does not mean that records should be falsified, but that recruiters should talk with applicants and encourage them to study and take the test again.

The recruiters' complaint against Davis "was the straw that broke the camel's back," Flaherty said. He did not supply specifics, but said that there have been other problems with Davis's command and that some of Davis's subordinates lacked confidence in him.

The chief said the recruiters, Sgt. Edward Adams and Cpls. Wayne Hemphill and Roland Wilson, did not tell anyone of Davis's alleged request until last week when they became angry over Davis's plans to transfer them out of the personnel department.

Davis said his problem with the recruiters began in 1982 or 1983 when he "raised holy hell" with those three officers, who he said had been involved in an attempt to reproduce a passing test paper of a black applicant because the original test paper had been lost. The three were given official reprimands for the incident, Davis said.

Davis said it was during that angry conversation that the officers decided to turn on the tape recorder and he talked to them about how to assist marginally qualified applicants by encouraging them to reapply. "If I said something else on the tape, it was in anger," he said.

Davis, who will be 55 on Sunday, is a retired Army lieutenant colonel who was hired as a civilian in 1976 to help the police department through a tumultuous period when it was criticized as being racist and brutal. He taught human relations courses to officers and in 1981 was appointed by former chief John McHale to the rank of lieutenant colonel.

"I believe that I have done the job that I was mandated to do," Davis said last night. He said when he came to the department almost nine years ago, there were fewer than 50 blacks on the police force. "Today we have 170" out of a force of about 900, he said.

Davis' departure comes at a time when there is tension in the department over demands made by black police officers who believe the testing and promotional system is unfair. So far the black officers, the county and the police union have been unable to arrive at a set of changes that is acceptable to all sides.