D.C. Police Chief Maurice T. Turner, acknowledging that the police department "mishandled" its surprise April 5 urine test for marijuana use, yesterday reinstated 24 of the 39 police officers he placed on leave last week.

Turner said at a news conference that he reinstated the 24 primarily because they tested negative in a follow-up screening for the drug and because most of them passed a lie detector test in which they denied using marijuana since joining the force.

Fifteen other officers remain on paid leave pending further investigation, although two have admitted using drugs and face dismissal, Turner said.

The reinstated recruits will be allowed to graduate today as part of the 165-member class of new police officers. The ceremony is scheduled for 10 a.m. at Constitution Hall.

Turner has been wrestling with the decision, and postponing it, for several days because of contradictory evidence about drug use among the probationary police officers, according to police sources. Turner had scheduled a news conference Wednesday but canceled it and did not meet with reporters until late yesterday.

Turner said he remains convinced that 39 officers among the recruit class were guilty of using marijuana. But because of "mix-ups" in urine samples, he added, "I can't identify the 39."

Based on a report from his internal affairs division, Turner said, "There appears to have been some type of mishandling of urine, and because of this we cannot say there is proof positive it was these 39."

Turner said he will "tighten procedures" for future marijuana testing, which he said will continue in recruit classes and also as part of routine physicals for officers.

Gary Hankins, president of the Fraternal Order of Police labor committee, said yesterday he thought Turner's intentions had been good in seeking to rid the department of marijuana users, but said the department used poor methods to do so.

Hankins said Turner was wrong to discipline the 39 based on the results of a single test, given April 5, before conducting a second test and a thorough investigation to confirm their drug use. The recruits were placed on involuntary leave and ordered to surrender their guns and badges on April 26, the day the test results were announced and the second test was given.

"I think the department was overzealous in its desire to keep itself free of rookies using drugs," Hankins said. "They had the right idea, but they should have given more attention to assure that the privacy and rights of people are protected until they were as certain as possible that they were accurate."

The urine tests detect drugs used within the last few weeks, according to experts, although Turner had mistakenly said last week that the testing could determine whether persons had used marijuana as long ago as seven years.

Confusion over the life span of the test led some officers and recruits to the conclusion that Turner sought to purge anyone who had ever sampled marijuana. D.C. police recruiting guidelines, however, do not prohibit the hiring of persons who have used marijuana.

Turner said he sought only to discipline those who had used drugs since they were sworn in Dec. 14 for the 21-week training course.

Turner has attempted to explain the discrepancy between the April 5 and April 26 test results by saying that recruits who were using marijuana prior to the first test had stopped smoking it. The time lapse between the two tests was long enough, he said, for someone who stopped smoking after the first screening to show a negative result in the second test.

Many of the recruits and several private lawyers representing them have protested that they were wrongly accused because urine samples were mislabeled and mishandled, Hankins said.

Attorneys and family members of the accused recruits have complained that Turner left them dangling until the day before their scheduled graduation.

As of late yesterday afternoon, the D.C. police academy had not yet printed the programs for the graduation ceremony, partly because of uncertainty over who was graduating, a spokesman said. "It's still up in the air. We haven't heard from downtown," he said.