Navy Corpsman Brent C. Patterson, whose written confession last fall triggered a wide-ranging drug investigation at the National Naval Medical Center in Bethesda, testified yesterday that Navy law enforcement officials led him to believe he could help his own case if he fingered drug users at the hospital complex.

At a general court-martial hearing in connection with drug, bribery and conspiracy charges against him, Patterson testified that he admitted drug violations and identified alleged drug users because Navy investigators told him they "had the book on me" and implied that "nothing I said would hurt me."

Defense lawyers in the case contend that Patterson's confession to Naval Investigative Services agents, following his arrest last September, was improperly induced, although the 21-year-old corpsman was advised of his right to a lawyer, and dictated and signed his statement. He testified that he initially asked for a lawyer but changed his mind when investigators started to take him to the brig.

Patterson said one of the reasons he agreed to talk was that NIS agent John O'Hara told him people had made statements against him. Patterson, who implicated 110 military personnel at the medical center as drug users, testified that O'Hara said to him: " 'You mean all these people have dropped the dime on you and you're not going to make a statement on them?'

"I had plenty of help after I started naming individuals," Patterson told the trial judge, Lt. Col. Richard Vogel, and the five-member panel convened at the Washington Navy Yard. "They the NIS agents thought it would be better and easier if I looked at an alphabetical listing of everyone in the medical center command."

In testimony, agent O'Hara denied making any promises to Patterson or pressuring him. NIS agent Kevin Kuhens testified that, on the contrary, Patterson "strongly desired to talk to us." He said Patterson volunteered to take a lie detector test to verify his statements.

Patterson is the first person to face a general court-martial as a result of the drug investigation at the medical center. The proceeding coincides with the Navy's worldwide effort to crack down on drug use in its ranks.

After the prosecution rested its case yesterday, Judge Vogel granted a defense motion to find Patterson not guilty on three of the marijuana charges. Three other marijuana charges were withdrawn when a witness could not be located. The corpsman still faces 21 counts of drug violations, bribery and conspiracy.

At yesterday's hearing, three corpsmen testified under grants of immunity that they had purchased small amounts of what was advertised as marijuana from Patterson at various locales around the medical center, including outside the Enlisted Men's club and in a supply room where Patterson worked.

Patterson's civilian lawyer, James Kolb, made a novel gambit with the Oregano and Parsley Defense, hoping to prove that the corpsmen wouldn't know marijuana from omelet seasonings. He introduced as exhibits B and C, two small bags containing oregano and parsley and asked witnesses if either of the exhibits was marijuana. None of the corpsmen was sure.