They swept through the hallways and classrooms of Merritt Elementary School once more last weekend, leaving potted plants muddying the hot orange carpeting, bulletin board pin-ups of admirable black men and women strewn across the floor and sixth grader Martin Wolfe's carefully penciled map of Central America ripped into tiny geometric shapes littering the floor around his desk.

It was the third time in two months that vandals had rampaged through the classrooms of Merritt Elementary School, an immaculate, five-year-old school sitting in sharp contrast to the dilapidated apartments and rundown city schools near Minnesota Avenue in far Northeast.Hardly anything of value is ever stolen, but the randomness -- and the senselessness -- of the destruction has school officials and students puzzled.

This time vandals climbed up the white concrete sides of the school to the third-floor music room and broke in through a window. There, they knocked over bulletin boards and kicked in the entire back panel of an electric piano. Then, with a screwdriver, they pried open the locked door to principal Bill Lipscomb's office and spread his personal papers and school forms all over the floor. Throughout the second and third floors they overturned desks and chairs and potted plants. They tore the turntable off a record player. They even smashed the painted turtle shell that sixth-grade teacher Judith Gee uses in her science class.

The only thing taken was a microphone used in school assemblies. But what was left was $4,000 in damage and the question: why?

"Our school probably looks gooder than their school," said sixth grader Russell Anderson, convinced like many other students that the vandals are from nearby junior high schools, not Merritt.

Although Merritt has been hit hard by vandals recently, it is hardly alone in its problem. The National Education Association says one-fourth of all American schools are vandalized every month.

The last time Merritt was vandalized, one seventh-grade student admitted he was involved with four other boys from nearby Roper and Woodson junior high schools. The youth, a soft-spoken 13-year-old in Adidas sneakers and well-pressed jeans, said he and the other youths simply were standing around on Friday night and decided they'd like to go to a Bruce Lee kung-fu flick at the Town Theater.

But three of the boys were broke. So they decided to break into the school to see what they could find to sell on the street.

Once inside, they smashed open a soda machine with a faucet they ripped from a water fountain, which spurted all over the ceiling and walls and kept on flowing until school officials discovered the mess on Monday.

"We didn't think nothin' of it," the youth said. "I don't really know why we did it. I guess the school is just easy to climb into."

The youths got only $2 from the machine and never did go to the movies that night.

Yesterday, students went on studying math and social studies as Officer Joseph Brenner poked around classrooms in a Columbo-style tan overcoat looking for clues.

"Does anyone know that the school was vandalized last night?" he asked a group of youngsters. All hands shot up.

"Does anyone know who did it?" All hands went down.

Meanwhile, Martin Wolfe was worrying about the map of Central America that was now in pieces. "I guess I'll ask the teacher if she has another one to give me," he said, so he can start all over again.