The $1 million fire at the University of Maryland grand ballroom was deliberately set, state fire marshal James C. Robertson said yesterday.

Robertson said evidence sifted from the spectacular Wednesday night fire revealed it to have an "incendiary origin," but he declined to say what type of device was used to start the blaze.

The ballroom and its adjacent lounge were empty when the fire began, but several hundred people in other parts of the Student Union Building fled the scene without incident. Many of them reported that manual fire alarms failed to sound during the emergency.

University police and state fire officials said they are pursuing several leads about the person or persons responsible for the fire, but were reluctant to release any details of the investigation.

"This type of case is as sensitive as a sexual assault; any slip could blow the case," said Sgt. Fred Pross, a university police spokesman..

The fire started shortly after 8 p.m. Wednesday, near a large wooden bar in the lounge, according to fire officials, and spread quickly into the 900-seat ballroom. Robert Ryan, who is in charge of fire safety at the College Park campus, said no one was authorized to be in either room at the time.

"They could have wandered in through an open window or door," said Ryan, who is investigating why some of the alarms failed to work. "The rooms were unoccupied, but I cannot say whether they were secured," he added.

Ryan said small fires have been set in the past as pranks, often by drunken students, but noted that, "the most severe was a one-room burnout about two years ago."

Ryan said all of the damage is covered by insurance, either through the university or the state treasurer's office.