About 700 pupils at Flint Hill Elementary School in Vienna got a firsthand lesson in safety yesterday when firefighters lecturing children on fire prevention alerted school officials to a possible gas leak and the school was evacuated.

The pupils were bused to nearby Madison High School for the day, but it turned out later that there was no gas leak.

Lt. Eugene M. Campbell of the Fairfax County Fire and Rescue Department said that firefighters, nearing the end of their lecture, were alerted by teachers to the possibility of a gas leak, and they discovered the fumes near an oven in the kitchen. School officials then decided to evacuate the school, he said.

"They were saying how to prevent fires and stuff," said Joanna Kosmides, 8, of the firefighter who spoke to her third-grade class as part of Fire Prevention Week. "Then the gas leak came."

Joanna, wearing a pink sweater and matching pink barrette, said she and her classmates were learning to "stop, drop and roll" in case of a fire when they found out "that our building was going to blow up."

Superintendent Patsy Costolo of Area 3 said she was meeting with school principals at the time, and they decided to move the pupils from 2444 Flint Hill Rd. to the high school about a block away, rather than send them home.

The elementary pupils appeared to be having the time of their lives spending the day with the older students. But the high school students looked at the situation a little differently. "We were in gym and we came out, and all these little kids were walking around," said sophomore Amy Treadwell, 15. "I think it's pretty weird. It never happened to me in elementary school."

After lunch in the Madison cafeteria, the young pupils were entertained by the high school's madrigal singers in the auditorium.

As the youngsters filed out for recess, Flint Hill Principal Linda Clark shook her head in amazement. "How do you move 700 kids? With a lot of help." But Clark was mostly proud. "I'm pleased," she said. "It shows we've taught them well," she said, looking at the neat rows of pupils on the lawn.

Clark said the school immediately informed the news media when the decision was made to move the students so parents would be alerted to the situation. A hot line was set up and signs were posted at the elementary school.

About 118 parents decided to retrieve their children by 2:30 p.m., an hour before school was officially let out, but most decided to leave them where they were. "We've had several parents come and say, 'Everything looks fine, let me know if I can help,' " Clark said.

Workers from Washington Gas Light Co. went to Flint Hill, but found no gas leak, said Sally Mann, a company spokeswoman. A school spokeswoman said officials speculated that the fumes were the residue from a faulty pilot light that had been repaired the day before, and said the school would be open today.