D.C. Police Chief Maurice T. Turner agreed yesterday to use lie detector tests and a follow-up urine test as bases for deciding whether to fire 39 police recruits who were relieved of duty Monday for alleged marijuana use, according to a police union official.

Turner made the agreement after meeting with Gary Hankins, president of the labor committee of the Fraternal Order of Police, who said he told Turner of several reports of sloppy test procedures and "mix-ups" in the April 5 urinalyses that led to the actions against the recruits at the police academy.

"There well may be 39 individuals who used marijuana at the police academy, but we have some real doubts that the 39 who were relieved are the ones who used marijuana," Hankins said after the half-hour meeting in Turner's office.

Turner could not be reached for comment. But a spokesman, Lt. Hiram Brewton, said the chief had not acknowledged any mix-ups in the original tests. Brewton said Turner could have fired the recruits, but instead had ordered the follow-up testing "because he is not reckless." He noted that the recruits, who make up almost one-quarter of the 165-member class at the academy, have not been suspended, but rather placed on "administrative leave" with pay.

At least 35 of the 39 accused recruits have denied using marijuana. Hankins said many of them told FOP officials that the April 5 testing was shoddy because some recruits were given sample bottles with their names on them, while other bottles were unlabeled and were not carefully handled after the sampling.

"There were mix-ups right on the spot and recruits had to correct their instructors regarding whose samples were whose," he said.

Meanwhile, Barry C. Stiller, an FOP lawyer, said yesterday that several recruits reported the same kinds of mix-ups on urinalyses that were administered last Monday after the disciplinary action. "It looks like the second test was screwed up, too," he said.

Several accused recruits have taken individual blood and urine tests, and in at least one case the test was negative, Stiller said.

Urine tests for marijuana, a process perfected only in the last several years, are generally considered more than 95 percent accurate, if properly administered, according to Dr. Richard Hawks, chief of research technology at the National Institute on Drug Abuse in Rockville.

Hawks also said that the most advanced testing methods can detect traces of marijuana in the body for only two months after use. Police officials, including Turner, said earlier that the test could detect marijuana use from prior years.

Hankins said that the union applauded Turner's desire to curb drug use, but added that "it would have been a more sensitive approach" to conduct the follow-up tests before imposing any discipline.

Results of the follow-up urine test are expected to be available today or tomorrow, while the polygraph examinations will be conducted this week, according to Hankins.

Abel Laboratories of Columbia, Md., conducted the lab testing and used three methods to check samples, Hankins said. Leon Wilson, president of the lab, would not discuss testing methods. But Hawks said the methods used, involving the use of radioactive isotopes and technologically advanced equipment, were the most accurate.

In another development, FOP officials and several recruits complained about the testing to Rep. Stanford Parris (R-Va.), who said through a spokesman that he had heard "horror stories" about marijuana testing from both D.C. police recruits and from Marines stationed at Quantico. Several hundred Marines there have been accused of using drugs, and some contend that the testing procedure was faulty, the spokesman said.

He said Parris had asked military officials for a report on testing methods and is "concerned" about the police situation.