A sleeping University of Maryland student was beaten and slashed about the head with a sharp instrument early yesterday by an assailant who had apparently crept through an open window of the woman's College Park apartment and into her bedroom.

The assailant was frightened away by a roommate in an adjoining bedroom who, awakened by the victim's screams, threw a chair against the closed door and herself began screaming.

The assailant is still at large, Prince George's County police said.

The victim, Sandra Lynne Hamblen, 21, a senior psychology student from Hillcrest Heights, Md., was listed in fair condition last night at the University of Maryland shock trauma unit in Baltimore, hospital officials there said.

She was flown there by a Maryland State Police helicopter after the 2:10 a.m. attack.

Dana Hamblen, the victim's father, said his daughter had suffered three six-inch-long slahses on her head and forehead and had been beaten about the eyes and nose. He said the slashes, which doctos think were done with a meat cleaver, ax or butcher knife, will cause permanent scars.

Hamblen also said his daughter had a possible concussion and was conscious, but unable to talk when he and his wife visited her at the hospital yesterday morning.

Hamblen was interviewed as he stood in the living room of his daughter's apartment in the two-story-gray, frame house at 4804 Calvert rd., College Park. While talking, he kept looking around the room, as if searching for some clue to the assailant's identity.

"She said she woke and saw this figure bending over her," Hamblen said. "She said he just started beating her.

"He would have killed her," he told one of his daughter's roommates, "if (the roommate who screamed) hadn't screamed. You all were lucky," he said, putting his arm around the girl's shoulders.

Sandra Hamblen's bedroom was one of three in the apartment. The bedroom door of the roommate who was awakened by her screams opens into Hamblen's bedroom.

Hamblen's roommates and neighbors said there had been no reports of prowlers in the area of largely single family homes where many university students live. However, the roommate whose bedroom adjoins Hamblen's said that about a month ago Hamblen was awakened by someone who was standing her window and flashing a light on her as she slept. The roommate said the person fled as Hamblen screamed.