General court-martial proceedings opened yesterday against the key figure in a wide-ranging drug investigation at the National Naval Medical Center in Bethesda.

Hospital Corpsman Brent C. Patterson, 21, has pleaded innocent to 23 counts of marijuana and cocaine charges, as well as bribery and conspiracy charges. Under the Uniform Code of Military Justice he faces a maximum of 48 years in prison and discharge from the Navy if convicted.

Patterson is the first to face a court-martial as a result of a drug probe by the Naval Investigative Services. That probe, which coincides with a Navy-wide crackdown on drug use, was triggered last fall when Patterson supplied naval authorities with the names of 110 servicemen and women at the military facility he alleged used drugs.

Patterson's civilian attorney, James Kolb, said the defense plans to contend that Patterson's confession was "involuntary." But in testimony yesterday before military judge Lt. Col. Richard Vogel and a five-member panel convened at the Washington Navy Yard, NIS agent Kevin B. Kuhens said Patterson "was never hesitant about providing a statement. He always expressed a willingness. His general overtone was that he was glad to get it off his chest."

Former hospital corpsman Robert J. Juliao, now stationed in Guantanamo Bay, Cuba, testified that as an NIS informant he received small amounts of cocaine from Patterson on three occasions in June, and arranged to buy 13 1/2 grams of cocaine from Patterson on Sept. 3. Juliao also testified that Patterson handed him a $100 bribe to alter the results of a urinalysis test of another corpsman.