Navy Hospital Corpsman Brent C. Patterson, 21, the key figure in a wide-ranging drug investigation at the National Naval Medical Center in Bethesda, was convicted of 15 drug and conspiracy offenses at a court-martial yesterday and sentenced to two years at hard labor.

A five-member military panel first returned its guilty verdict, then reconvened and deliberated about 3 1/2 hours before deciding on the sentence, which included a reduction in pay and a bad conduct discharge. The panel also recommended that six months of the prison sentence be suspended.

Patterson, who could be eligible for parole in less than a year, could have received up to 17 years in prison and a dishonorable discharge.

"I'm relieved," said Patterson before he was led away in handcuffs. He had rejected a prosecutor's offer of a recommendation for a three-year prison sentence in exchange for a guilty plea.

His parents, Calvin and Cynthia Patterson of High Point, N.C., attended the court-martial in a courtroom at the Navy Yard in Washington. "I was prepared for something a whole lot worse; it could have been a whole lot worse," she said.

After his arrest last September, Patterson triggered an investigation at the medical center when he gave a written statement identifying nearly 100 military personnel there as drug users. In that statement, he also asserted he was responsible over an 18-month period for 70 percent of the drug traffic at the sprawling medical complex.

In a statement to the court, Patterson attributed much of his drug involvement to "peer pressure." He said, "I realize I have been wrong . . . . I feel I have reached a turning point and from here on out will use better judgment in choosing both my friends and also who I listen to."

Patterson was found guilty of possessing, selling and transferring cocaine on four occasions between last June and September. He was also convicted of selling and possessing marijuana in two instances and three counts of conspiracy, including one charge that he conspired to have a fellow corpsman alter the result of a friend's urinalysis drug screening test at the hospital complex.

Patterson, who was the first person to be court-martialed as the result of the investigation he triggered, based his defense on the contention that his confession to Naval Investigative Services agents Sept. 3 was involuntary. During the court-martial he testified that he had initially asked to see a lawyer but was pressured into making a statement.

NIS agents disputed that and said that Patterson had even volunteered to take a lie detector test to verify his statements.

Patterson, who had already spent 101 days in the brig at the Quantico Marine Base, appeared high spirited and happy-go-lucky throughout his trial. His mother testified he "had never been in trouble in his life," but he was "immature for his age" and in "many ways was like a kid."

His conviction will be automatically reviewed by the admiral who ordered him court-martialed.

Patterson's trial was a general court-martial, the most serious judicial proceeding against a serviceman. Three special courts-martial arising from the drug investigation are scheduled for next week. Personnel convicted at those proceedings may be sentenced to no more than six months' imprisonment and a bad conduct discharge. Prosecutors expect as many as a dozen additional special courts-martial to be convened in the next few weeks.