Pleading for his life, a black sailor from Suitland told a military panel in Newport, R.I., yesterday that "a strange feeling came over me and I just snapped" the day he murdered his white superior officer at sea.

Petty Officer 3rd Class Mitchell T. Garraway Jr., 22, testified that a combination of pressures -- including tension over racist attitudes in his division and sorrow over the recent death of his grandfather -- led to the stabbing of Lt. James Sterner June 16 aboard the frigate USS Miller near Bermuda.

The same eight-man panel that convicted Garraway Jan. 30 of premeditated murder is now hearing testimony on whether the sailor should be sentenced to death or to life in prison.

The Navy last executed one of its own in 1849.

By putting Garraway on the stand, defense attorney Trevor L. Brooks of New York said he is trying to show that extenuating circumstances made his client's crime no less tragic but more understandable, Washington Post Special Correspondent Judy Rakowsky reported from Newport.

In a barely audible voice, Garraway told the quiet, tense courtroom at the Naval Education and Training Center there that he rarely had contact with Sterner, a former Prince William County school teacher, and never planned to harm him.

"I usually lift weights to get rid of tension and stress," he said, "but that night, it didn't do any good."

He walked around the ship, he said, and wound up in the passageway where he encountered Sterner.

The officer was stabbed in the back with a Marine combat knife and bled to death in the corridor.

"It just happened so fast," Garraway said. "I grabbed him and that's when I stabbed him. I was mad at myself for doing it. I felt real bad."

During his 1 1/2 hours of testimony, Garraway described an unhappy childhood and frequent beatings he said he received from a stepfather he described as brutal and demanding.

He also dwelt on his shock at the racism he said he encountered aboard the Miller. He was the only black in the ship's engineering department, Navy officials said. The ship had a crew of 195, of whom 30 were black.

Garraway said his name appeared under bathroom drawings of men with "enlarged lips and Afros." He also recalled one message apparently referring to him that said, "Someone has to tell this nigger how he's supposed to deal."

Garraway said he had had heated arguments with his supervisor in the engineering department, Petty Officer James Fields, about racist remarks that Fields allegedly had made.

He also said Fields blocked a promotion he deserved and denied his requests for leave to attend his grandfather's funeral and to visit his father, who was hospitalized for open heart surgery.

In earlier testimony Wednesday and yesterday, a dozen character witnesses, including Garraway's mother, Mattie Umrani of Suitland, described the sailor as a quiet, respectful man.

"He's what people characterize as a nice guy," said Petty Officer Belkis Pineyro, who described herself as a close friend.

"I thought that he was a scapegoat," she testified. "He was very proud to be on that ship. It had the best crew."