Seniors at North Rockland High School did something yesterday that most haven't done since elementary school: They rode their bikes to class.

The classwide bike ride -part senior class prank, part environmental awareness and part protest - was designed to bring attention to rising gas prices and the effect they are having on young people, students said.

"Gas prices are ridiculous," said Kimberly Ceccotti, a senior from Stony Point. "Most of us work part time and now we can't even fill the gas tank."

She and other upperclassmen decided to leave their cars in the driveway and dust off their bicycles to get to school to show their frustration with fuel prices that are hovering around the $4-per-gallon mark.

Word of the bike ride started to circulate among students several weeks ago and was spread from student to student by e-mail and text message.

"We waited all this time until we were seniors so we could have the privilege of driving to school," said Amanda Amoroso of Stony Point. "Now we can't even afford the gas."

North Rockland isn't the only school in the area hoping to bring attention to the issue of high gas prices.

Students at Clarkstown High School South in West Nyack are planning to ride their bikes, walk or take the bus to school tomorrow.

Clarkstown South senior Mike McQuillan started riding his bike to school three weeks ago. Since then, 10 friends have joined him. Now McQuillan is hoping the entire school will do it tomorrow in a schoolwide "Tour de South."

"You get less emissions, less cars on the road, less cars in the parking lot," he said. "It's good for the environment."

McQuillan is finding that riding his bike 2 1/2 miles to school as well as on errands and to friends' homes is having other benefits as well: He said he has lost 12 pounds.

Students at other schools throughout the region are rediscovering bicycle riding as a way to get around, said Wiley Norvell, spokesman for Transportation Alternatives, a New York City organization that encourages people to use alternatives to cars.

"The driving culture is so ingrained in people - especially teens - that it's great to see them realize that they can have freedom and mobility without using their cars all the time," he said.

Few students said they would consider another environmentally friendly means of getting to school: the familiar yellow school bus.

"No one wants to ride the bus," said Patrick Chavis, a senior from Haverstraw, who yesterday rode a bike for the first time in four years.

North Rockland school officials had heard talk about the bicycle plan, but even so, they were surprised to see more than 150 students riding up to the building on two-wheelers yesterday morning, Superintendent of Schools Brian Monahan said.

"I'm proud that they are doing this," he said. "But I'm also concerned about their safety."

School officials were in touch with the Haverstraw police to make sure roads near the school were well-patrolled at dismissal time.

Only seniors are allowed to drive to the school. North Rockland issued 250 parking permits to 12th-grade students this year, Monahan said.

The school is a closed campus, and students are not allowed to leave during the day.

When students arrived yesterday morning on their bicycles, they had hoped to leave them in their assigned parking spaces, Ceccotti said.

But school officials decided that was too dangerous and had the students park their bikes in back of the school.

At the end of the school day, students lined up in the rear of the building and waited for dismissal.

"This is a great way to save gas and go green," said Ray Lopez, a senior from Haverstraw.

Even the students who didn't take part in the classwide bike ride said they wished they had.

"I would have, but I don't have a bike," said Kyle Schepis of Stony Point as he got into his 2003 Nissan Ultima. "I'm spending $85 a week in gas - it's crazy."