Keith J. Gardner pleaded guilty yesterday to murdering his parents and grandfather, as Fairfax prosecutors revealed new details about the stabbings at the family's Lorton home and the anxious search for the victims in May.

Gardner, 39, faces a minimum of 20 years and a maximum of three consecutive life terms without parole at a sentencing hearing that Fairfax County Circuit Judge Marcus D. Williams scheduled for Dec. 10.

In court yesterday, Gardner admitted fatally stabbing his parents, Jimmy and Jannis Gardner, and his grandfather Elmer inside their home in the 9200 block of Gilmore Drive in Lorton. The bodies were found May 11, but police believe they were killed April 30, then dragged to an underground fallout shelter and covered in limestone powder.

After the slayings, Gardner fled to Florida, but he continued to use his parents' credit cards, said Commonwealth's Attorney Robert F. Horan Jr. When Gardner was arrested by FBI agents and local sheriff's deputies near Pensacola, Fla., on June 1, Horan said, his only statement about his motive was that "he was a heavy drug user, and drugs made him do things that humans just don't do."

Autopsies showed that the three victims had been stabbed repeatedly and that their throats had been cut. Horan said there was no indication that any argument or conflict preceded the killings. DNA testing on clothing found in Gardner's bedroom detected his mother's blood on a pair of jeans and his grandfather's blood on one of his boots, Horan said.

After speaking with Gardner's family members, who opposed the death penalty, Horan made an offer to Gardner: Plead guilty to three counts of first-degree murder, and Horan would not seek the death penalty.

Gardner agreed, and two days after his indictment Aug. 16, his attorney announced Gardner's intention to plead guilty.

"If the family had had a different view," Horan said, "I would've tried him for capital murder in a heartbeat."

Kim Gardner, Keith Gardner's older brother, said he and two of his uncles told prosecutors last month that "the death penalty wouldn't bring my parents back" and that they favored a quick resolution to the family's trauma.

Friends and neighbors last saw Jannis Gardner, 63, Jimmy Gardner, 64, and Elmer Gardner, 90, on April 29, Horan said. Concern grew when they were not seen over the next few days, and Jannis Gardner uncharacteristically missed church May 2.

Keith Gardner was seen periodically around his parents' home, and told Kim Gardner that their parents had gone to Arkansas. Meanwhile, Horan said, Gardner collected $1,350 in rent from two tenants who lived in apartments connected to the Gardner house.

After friends noticed Jannis Gardner missed church again on May 9, Kim Gardner, while on vacation in Florida, asked a friend to break into his parents' home. But the friend found nothing amiss, Horan said. Kim Gardner then learned from relatives that his parents were not in Arkansas and asked neighbor Billy Rogerson to check the house.

By then, Rogerson said yesterday, Keith Gardner had noticed the break-in and asked Rogerson about it. Rogerson knew nothing, but when he got a call from Kim Gardner, "I went out back. I don't know what made me go to it. I went to the shed."

Another neighbor, David Miller, went with Rogerson, and inside the shed, they noticed heavy caulking around the fallout shelter doors. They tried to pull the doors open, but the handle broke off. Finally, with a crowbar, they pried open the shelter. "I knew as soon as we opened it up," Miller said.

Gardner showed no emotion as Horan recounted one of Gardner's other statements to the arresting officers in Florida: "He stated he loved his parents, and his mother had been as good as gold to him. He stated he couldn't believe he'd done something like that to her."

Connie Quinn, a longtime friend of the family, wept during the hearing, and she said Lorton neighbors favored the death penalty for Gardner. "He's getting away with murder, being in jail," Quinn said.

CAPTION: Keith J. Gardner, 39, could be sentenced to three consecutive life terms for the three murders.