Army Staff Sgt. Terry Lee Simmons, accused of killing his girlfriend and their infant daughter in their Baileys Crossroads apartment, was found guilty last night of the second-degree murder of his girlfriend.

A Fairfax Circuit Court jury deliberated 5 1/2 hours before returning its verdict and recommending a 20-year prison sentence, the stiffest penalty allowed for second-degree murder -- killing with malice but without premeditation. Simmons, 27, who had sobbed uncontrollably at times when he testified on Thursday, sat ramrod straight and appeared unemotional as the decision was read.

Before the case went to the jury yesterday, Judge Richard Jamborsky dropped the count charging Simmons with the death of his 3-month-old daughter, Julie, on the basis of unsufficient evidence.

The decomposed bodies of Caroline Yoo, 29, and Julie Simmons were found on Aug. 16, in a walk-in closet in the couple's $400 a month, two-bedroom apartment after neighbors complained of foul odors and saw hundreds of flies inside the apartment windows. Authorities said the mother and daughter had been dead since June 19 and that Yoo's neck was bruised and the child's skull fractured.

In the closet with the bodies were more than 20 pine-scented air fresheners, moth balls, a pan of disinfectant and several incense burners, according to court testimony.

Simmons, who stayed in the apartment several days after the slayings, then with friends before going on a vacation to Canada, fled to Florida after returning to the apartment and finding that it had been sealed by Fairfax County police. According to testimony, Simmons turned himself in to military police at Fort Benning, Ga., on Aug. 20.

Simmons testified that Yoo, who was born in Korea, felt "ashamed that she had had a child with an American GI and felt she could never face her parents again." He said it was Yoo, not he, who had killed Julie, and that his discovery of the dead child's body in her crib had triggered the events that led to Yoo's death. Although Simmons had said, in a statement made at Fort Benning, that he had "choked" Yoo to death, he testified at his trial that he could not remember the incident.

Fairfax Commonwealth's Attorney Robert F. Horan Jr. sought two first-degree murder convictions. But yesterday, defense attorneys Jonathan Thacher and James Harney asked the judge to drop the count charging Simmons with his daughter's death, arguing that Horan had not "presented one iota of evidence that says that Terry Simmons is responsible for Julie's death."

Horan countered that if the jury were to accept the premise that Simmons' murder of Yoo had been premeditated and that Simmons wanted to "rid himself" of an "entanglement" with her, then it could possibly follow that "he had to kill Julie too."

After clearing the jury from the packed courtroom and listening to arguments from both sides, Jamborsky retired to his chambers for five minutes to consider the motion, then decided in favor of the defense. The judge also ruled that the jury would not be told of the decision until after they deliberated the murder charge in Yoo's death.

Sentencing is set for Dec. 18.