Fire officials ordered Anacostia High School in Southeast Washington closed yesterday after the third deliberately set fire in two months broke out, and both the fire alarm and a back-up warning system failed to work, according to authorities.

More than 1,700 students and school personnel were evacuated after school administrators went from classroom to classroom to sound an alert shortly after 11:30 a.m. yesterday, according to Principal Clyde Gray. No students or school personnel were injured in the fire, the first of the three to occur during school hours.

D.C. Fire Battalion Chief Ray Alfred, the department spokesman, said the school will be closed at least today and until officials are certain there is an adequate alarm system so "students' safety is not at risk."

A D.C. School Board spokesman said yesterday that repairmen had been sent to check the system, but it had not been determined whether the school, at 16th and R streets SE, would reopen tomorrow. "I'm sure we will have to pass a fire inspection," said spokesman Janis Cromer, who added that officials hoped to reopen tomorrow.

She also said the board had ordered new security precautions, though she would not elaborate.

Yesterday's fire broke out in the school auditorium, destroying some of the curtains on stage and causing an estimated $50,000 damage, according to Alfred. The fire was extinguished "in a couple of minutes," according to Deputy Chief Michael C. Tippett, but it "generated an enormous amount of smoke."

The smoke was so thick, he said, that two firefighters fell from the stage. Sgt. John Wooten was treated for a sprained ankle and firefighter Garland Graves was treated for a shoulder injury. Neither was hospitalized.

Alfred said the fire was "definitely arson" -- the same finding that has been made by investigators for a Dec. 15 fire that caused $200,000 damage to the school's kitchen and cafeteria, and a spate of fires Dec. 24 that caused about $100,000 damage to numerous classrooms. Those fires were set when the building was closed.

No arrests have been made in any of the three incidents.

"Even though the two previous fires involved more damage . . . when kids are there it causes a lot more concern," said Cromer. "The potential for harm is greater."

Gray said investigators previously did not think the arsonist was a student, but that it might be "a possibility." He said "it might have been done to disrupt . . . when you have 1,600 youngsters, who knows?"

Cromer said there were conflicting reports yesterday, some saying the alarm system was not working and one report that it had been turned off.

Several students interviewed outside the school said they heard no alarm and knew of no backup system to alert them to fires. "We don't have fire alarms, and if we do they don't ring," said Kaylana Byrd, a senior. "We have not practiced fire drills . . . . You just find a door and get out."

Gray said the alarm is "inoperable. I can't guess for how long." He said that as a backup, a single extended bell is to ring for fires, but that bell did not work yesterday. Neither did the school's public address system, he said.