A 22-year old Quantico Marine sergeant was sentenced to a long prison term at hard labor yesterday after admitting to the murder of a female Marine captain, a crime a prosecutor characterized as "murder most foul . . . a virtual execution."

Sgt. Charles D. Owens pleaded guilty to premeditated murder and told a military judge at the Quantico Marine Base that he strangled Capt. Patricia M. Barnett, 33, during an attempted burglary of her quarters on the Quantico base on May 7.

Although Marine Lt. Col. John E. Grant, acting as judge, pronounced a sentence of "hard labor for the length of your natural life," Owens will serve no more than 50 years as a result of a pretrial agreement, and he will be eligible for parole from the federal penitentiary at Fort Leavenworth, Kan. in 10 years. He was also sentenced to a dishonorable discharge, demotion to private and forfeiture of all wages and benefits.

Owens was duty officer assigned to Liversedge Hall, where Capt. Barnett was living while attending a two-week computer training course on the base. Barnett, a nine-year Marine veteran, was regularly stationed at Camp Lejeune, N.C.

Barnett caught Owens attempting to burglarize her possessions about 2 a.m. and began struggling with the sergeant, resisting him violently, according to courtroom testimony.

The struggle moved from Barnett's room to an area near the building's mess hall, then to two storage rooms.

Owens, tears streaming down his face, testified that "I just wanted her to die . . . After she tried to hit me, she started to struggle again. There was blood everywhere and I got so involved that I just wanted to get it over with, so I choked her . . .

"She just kept struggling. She just wouldn't die," Owens said.

Barnett's body was found the next day in a wooded area near the residence hall. A Navy pathologist testified that an electrical cord and bootlaces were found nearby and that Owens probably used them to drag the body to the site. He also testified it appeared that the body had been washed clean of blood.

Maj. Michael Osajda, the Marine prosecutor, made the characterization of "murder most foul" and said: "Owens was charged with the duty to guard the officers in Liversedge Hall and this was a gross disgusting violation of that charge."

Owens, who joined the Marines five years ago, was described by a character witness as a "good influence on other Marines, a sincere young man and a loving father" to his three children.

Defense attorney Maj. Charles D. Breen asked Owens during the trial: "You killed Capt. Barnett; how will you live with this?"

"All I have to offer is my very deepest apology," replied Owens. If I could with my own life restore hers, I would do it."

Under military law, the case will automatically be appealed to Quantico's commanding general, then to the Navy Court of Military Review in Washington.