A 20-year-old Annandale youth, responding to his mother's frightened screams, was stabbed twice by a masked intruder who slipped into the family's first floor bedroom early yesterday morning, brandishing a large hunting knife.

Blaine Demico, of 7702 Kalorama Rd., was in serious condition yesterday at Fairfax Hospital after being stabbed in the chest and abdomen by the predawn prowler. Fairfax County police said yesterday they had no suspects in the case.

"I thought at first I was dreaming," said the youth's mother, Elke Demico, who has lived on the quiet, suburban street with her three children since 1966. "It was very, very scary. Blaine protected me," she said tearfully. "I can't believe it."

Demico said she had gone out for the evening Saturday while her two sons, Blaine, a junior at Norther Virginia Community College, and 12-year-old Anthony watched the Pittsburgh Steelers-Dallas Cowboys football game on television. The game ended at midnight. When she returned home, Demico said, she found Anthony asleep on the bed.

Demico said she went to bed, not realizing that her other son, Blaine, had fallen asleep on the floor beside her bed. She also had not realized that the side door to the family home had been left unlocked.

"I woke up about 3:30 in the morning," she said yesterday, "and saw a man standing at the foot of my bed. He was holding a large knife and had a pair of panty hose over his head. I started to scream. All of a sudden, I saw my older son leaping over the bed. There was a scuffle, Blaine fell under him."

Elke Demico said she was amazed to find herself on top of the struggling men, trying to pull the stocking off the intruder's head. "He didn't want me to pull it off," she said. "When I did, he bit my hand. Then he lost control of the knife an I got it away from him. The blade cut my hand. I couldn't see his face, just the back of his head."

The intruder, who Demico described as a young man of about 20, with curly brown hair and wearing a T-shirt and cut-off blue jeans, ran from the bedroom. Blaine Demico, bleeding from two stab wounds, ran after him. But the prowler, who Demico said must have entered through the unlocked side door, escaped on foot.

"Blaine said he had never seen him before," Demico said, choking back tears. "We've never done anything to anybody."

Elke Demico, a German-born, self-employed seamstress who is divorced, sat in her red brick home on the quiet, tree lined street yesterday comforted by neighbors who said they were appalled by the incident. "Nothing like this has ever happened around here before," one neighbor said.

Robbery, Demico surmised, was not the motive. "If he wanted to, he could have taken lots of things that were just sitting out. Money, jewelry, sculptures, paintings. I don't know what he wanted."

Demico said her 15-year-old daughter was out of town for the weekend. Blaine Demico underwent surgery yesterday morning. Asked why her son fought with the intruder, Demico said, "In a situation like that, you don't think. He's been such a good son. He's very beautiful."