D.C. Superior Court will begin to test for drugs all juveniles awaiting trial in an effort to stop drug abuse in its early stages, court officials announced yesterday.

The drug testing program for all juveniles arrested on criminal charges will be in place by October, according to Kathryn Boyers, project manager for the Drug Detection and Monitoring Program. Currently, drug testing for those under age 18 is limited to those detained overnight and are willing to be tested and to those ordered by a judge to submit to testing. There has been an adult drug testing program for two years. The testing will be done by Pretrial Services Agency.

The agency's preliminary research has determined that over 61 percent of detainees 18 to 25 years old test positive for one or more drugs, with cocaine and PCP being the most frequently detected.

Superior Court Chief Judge Fred B. Ugast said, "The importance of the testing is that it will help judges make more informed and intelligent decisions when the juveniles come before them initially." And, he said, the testing will help "in terms of placement of the juvenile" into treatment programs.

"The new program will help us determine the effect of intervention in early stages," Boyers said. "One of the major outcomes, once we've identified juveniles using various controlled substances, will be to ask ourselves 'What happens next?' " She added that more drug treatment programs will probably be needed.

Meanwhile, Tuesday has been proclaimed "Drug Free D.C. Day" by Mayor Marion Barry, with a large antidrug rally at noon, with celebrities and free refreshments at 14th and W streets NW, in the midst of the city's worst drug trafficking corridor.

Although both programs have been in the planning stages for some time, the announcements came a little more than a week after Maryland basketball superstar Len Bias died of cocaine intoxication and at a time when public concern about the city's drug epidemic has heightened.

"The recent unfortunate death of Len Bias has made the public aware of the fact that cocaine can kill, and PCP is destroying the minds of our youth," Barry said in a press release on the rally. "To say nothing can be done about the problems of substance abuse in our city is a myth."

On "Drug Free D.C. Day," Barry will announce the expansion of treatment centers, said Dr. Andrew McBride, D.C. commissioner of public health, at a news conference yesterday. Muhammad Ali, singer Stacy Lattisaw, entertainer Chuck Brown and former Washington Redskin George Starke are expected to participate in the rally, McBride said.

Local bands and street groups will perform and T-shirts, buttons and information on drug abuse will be given away. People who want drug treatment can sign up for programs, McBride said.

The rally will be the first of several. On July 27 a special prayer day will be held in 150 churches, he said, and on July 31 there will be a citywide program for the elderly, to tell them what they can do about drug abuse in their communities.

"We know in Washington this problem will not go away without the active participation of everyone -- a joint public, private and community effort," McBride said.