Lee Mariggio, 13, does not like school, but he loves riding minibikes. And as he sat blinking in the warm spring sunshine, he tried to explain why.

"I love 'em, except when you wipe out," he said. His mud-caked corduroy jeans are evidence of an earlier spill. "It's a big deal. It gives me something to look forward to after school."

Mariggio's likes and dislikes are similar to those of the other 19 junior high school students in the Bethesda YMCA's National Youth Project Using Minibikes, or NYPUM. A strictly voluntary program, NYPUM was set up for students who do poorly in school work or have problems in relationships with other teen-agers.

Counselors and students twice weekly commute to the Upper Montgomery YMCA in Gaithersburg, where they ride donated minibikes over six acres of dirt trails and bike jumps.

"When these kids get out of school after a full day, they're full of energy," Brager said. "It's amazing what an hour on a bike can do."

Minibikes are small, stripped-down versions of motorcycles that travel up to 40 miles per hour, Brager said. Unlike street cycles, minibikes have knobby tires for traction on dirt.

Most of the students are referred to the program by their teachers or counselors. Once they enter NYPUM, which continues throughout the school year, they must participate in weekly discussions with their peers and YMCA counselors.

Following rules developed by the group, the groups essions are intended to help youths deal with their problems and achieve mutual goals.

"Everything said in the group is confidential. No putdowns. Fights cost you 5 to 10 minutes of riding," recited Mariggio, winner of a recent YMCA Partners in Youth Minibike Marathon.

While Brager says the program is generally approved by parents, some question whether minibikes are a constructive channel for youthful energy.

"If he insists upon doing it, I'd rather he do it under (YMCA) auspices," said Mary Ward, whose 14-year-old son is in the program. "Personally, I don't like this sort of thing."

But Brager insists the students are carefully trained and supervised on the bikes. Over the past four years, the worst injury has been a broken leg, a safety record Brager contends is reasonable.

A problem for minibike riders has been the continuing decrease in the number of public riding areas.

The tract used by the YMCA is one of the few areas in Maryland that is legally open to minibike riders.

"I haven't seen a vast increase in the use of bikes, but it continues to boom," said John Jones, a Montgomery County police community affairs officer.

Jones said most complaints about the bikes concern the noise they make. In Gaithersburg, NYPUM has prohibited bike riding after 5 p.m. becaue of complaints from a housing subdivision nearby.

But the biggest problem for the police is catching youths who use the bikes illegally, Jones said. Police vehicles are usually not equipped for travel on dirt, and it is illegal to ride mini-bikes on the streets.

Jan Weiffenback, whose son is in the program, says she feels the program is safer than other sports, such as football.

"Jay has been taking summer minibiking (at the YMCA) since he was 10. It's something that he does well," she said. "If he didn't do it at the Y, he'd be on the street doing it illegally."