A late morning fire that investigators said was deliberately set by a student caused $250,000 in damage to the Douglas MacArthur Elementary School in Alexandria yesterday and forced the evacuation of 598 students and 41 staff members.

Two students at the school were questioned as suspects in the blaze -- described as the worst school fire in the city's history -- but no charges were filed by last night.

No one was injured. The blaze destroyed four classrooms and damaged four others at the school at 1101 Janney's La. The school will be closed today and a decision will be made by noon whether any part of the building will be reopened on Thursday.

"We feel the fire was deliberately set, and we believe one of two students set it," city fire marshal Randolph Kirby said. "We don't know how it was started, or what materials were used, but there was a tremendous fire in progress when we arrived," Kirby added.

The blaze melted sections of the school roof, weakened brick walls and sent acrid clouds of black smoke throughout the building, he said.

Betty Rich, a secretary in the school administration office said, "We heard the barest explosion coming from [a] classroom, and then one of the custodians ran in to say there was smoke in the back rooms." When a teacher ran in with the same report, Principal Lucy Kirby rang the fire alarm and spoke on the public address system to make sure everyone was moving out of the building, officials said.

Virginia law requires schools to hold four fire drills in the first month of each term and one drill each month during the rest of the school year, fire officials said. Yesterday the students were out of the building in less than two minutes, they added.

"Everyone thought it was a regular old fire drill until Mrs. Kirby came on the PA system," said Mark Moreci, an 11-year-old sixth grader, who bicycled back to the school yesterday afternoon to watch workmen board up damaged classrooms. "We came out without our coats and books. Some of the kids were upset, but most of them were happy. When you're a kid you wish the school would burn down, but when it actually happens you're unhappy because all your stuff is inside," he said.

Other children playing nearby said students and their teachers formed lines on the sidewalk, and watched as city fire crews battled the blaze for more than an hour.

According to Assistant School Superintendent Donald E. Dearborn, the 83 third graders assigned to the four destroyed classrooms were eating lunch in the cafeteria when the blaze broke out just before noon. The 91 sixth graders assigned to the four less severely damaged classrooms were studying in other parts of the building, Dearborn said.

The school has 32 classrooms, most of which were built in 1942.