Mayor Marion Barry assembled more than 100 D.C. government officials in the halls of D.C. General Hospital yesterday to ceremonially open the city's new 20-bed PCP detoxification unit.

Barry, who cut a red ribbon to mark the opening, said the city plans to add enough drug treatment beds by mid-August to accommodate about 250 persons now on a waiting list for treatment.

The PCP clinic opening is the latest effort in Barry's high-visibility campaign to respond to sharp increases in drug arrests and growing public concern about drug abuse.

Barry, a candidate for reelection this fall, said at a news conference, "There will be those who say this is a political year, a political move. I don't care what they say."

Citing a $5 million increase in drug and alcohol programs in the last year, Barry asserted that the city's $22 million budget for the programs is "the largest per capita expenditure for alcohol and drug abuse in the country . . . which means we are serious about this problem."

The mayor also hinted that the city will be aggressive in setting up new treatment facilities -- even if neighborhood groups object. The Barry administration has encountered stiff resistance from community residents whenever it has proposed new drug treatment facilities and halfway houses.

"The communities will have to allow us to put treatment facilities into our neighborhoods," Barry said, adding that officials would try to locate such centers close to neighborhoods with the most serious drug abuse problems.

"If drug users come from these wards, it will be neighbors' responsibility to welcome them back home . . . . It is like the war -- bring the boys back home."

J. Theodore Brown, director of the new PCP clinic, led the mayor and other officials on a tour of the facility, which has been designed to handle users of phencyclidine who exhibit the typically violent effects of the drug, an animal tranquilizer. Brown said the facility's staff has received extensive training in managing violent patients. In addition to treating users, the unit will have a toxicology laboratory designed to analyze street samples of the drug.

"I would not be so presumptuous as to say this clinic is the solution to the PCP problem," Brown said. "But it is a major first step and a remarkable one."

Hospital officials and representatives of the D.C. Alcohol and Drug Abuse Services Administration, who will jointly operate the clinic, released data on the PCP problem showing a high incidence of PCP use among those arrested for various offenses between March 1984 and March 1985.

In that period, 54 percent of arrested D.C. residents tested positive for PCP use.