Several hundred students were evacuated from the University of Maryland's Student Union last night as a two-alarm fire destroyed much of a grand ballroom there, causing damage estimated at $1 million or more.

Two firefighters suffered minor injuries in the blaze, which broke out about 8 p.m. Thick black smoke filled the massive, 30-year-old brick building, hampering firefighters' initial efforts. Answering the alarm were 120 firefighters from nine departments.

Several students who were in the building when the fire broke out said they did not hear fire alarms. Some said the manual fire alarms failed to work when pulled.

Carl Cimino, fire ground commander for the College Park Volunteer Fire Department, said "It's certainly possible the alarms weren't working properly, but I just don't know." He added that the manual alarms are only interior warning systems; notification of the fire department must be made by phone.

Robert Ryan, spokesman for the university's Safety Office, said there was no way to determine when or which alarms were sounded. He also said that while most of the Student Union has a sprinkler system, the ballroom did not.

Ryan said the cause of the blaze was not immediately known and arson had not been ruled out. The fire may have started in a small room adjacent to the ballroom, located in the east wing of the facility, he said.

Firefighters speculated that the damage to the ballroom was so extensive because it has hardwood floors and was not in use at the time the fire started. The room could have been blazing before anyone knew it was on fire, they said.

Although no precise estimate of damage was available last night, Tony Bizjak, assistant chief of the College Park Fire Department said, "You're probably looking at a million dollars damage to the building and another two hundred thousand to the contents."

Fire Chief Fred Brower said firefighters had problems unwinding and stretching their hoses through the three-story, neocolonial-style building. Among facilities housed in the Student Union are a bookstore, movie theater, record store, several restaurants and meeting rooms. The ballroom was added to the structure in 1972.

Monica Wilfong, a university junior majoring in meteorology, said she was attending a financial aid forum with about 50 other people, including University President John Toll and University Vice Chancellor William Thomas, at the union last night. "A lady came in and said there was a fire two rooms down, but nobody moved at first. Then the lady yelled. Nobody panicked, we just left the building."

John Hoagland, director of the Maryland Fire and Rescue Institute, was eating at one of the restaurants in the building when the evacuation began. "The staff people did a fine job of evacuating the people from the building," he said.