SAN MATEO — City officials may decide Tuesday whether or not residents under the age of 18 can be fined up to $500 for "loitering" in public places during school or late night hours, officials said.

The City Council is slated to vote at its regular meeting Tuesday whether to approve new rules on youth curfew hours. Officials say it's a way to keep at risk kids on track, but critics say curfews don't work and may make matters worse.

The new ordinance in San Mateo would target teens who "loiter" between 8:30 a.m. and 2:30 p.m. while school is in session, said assistant city attorney Bahar Abdollahi. Loitering is "lingering aimlessly in a place without a legitimate purpose," according to the ordinance. The rule also prohibits loitering between 11 p.m. and 5 a.m. from Sunday through Thursday and 12 a.m.-5 a.m. on Friday and Saturday, Abdollahi said.

Teens would face a written warning the first time they are caught and then a subsequent fine of $100 if caught violating curfew again. If busted more than three times in one year, the fine climbs to $500.

There are plenty of exceptions to the rule, however. Teens who are with a parent or guardian, driving a car or riding public transit, working or volunteering and on their way to or from school or an event don't have to worry about getting in trouble. Emancipated minors, teens responding to an emergency and young people near their homes are also exempt.

It's kids who are skipping school or hanging out on the streets at night that could find themselves in trouble, said San Mateo police Lt. Mike Brunicardi.

He said the department has a lot of programs to keep kids busy, such as the Police Activities League. But for those who still choose to hang around in public during curfew hours, the new rules would give police some enforceable consequences, he said. Approximately 80 percent of police contact with kids happens at night and the other 20 percent is between 8 a.m. and 4 p.m., according to a staff report.

"Our goal is to reach out to at risk kids," he added. "And steer them away from crimes that would land them in front of juvenile justice."

San Mateo already has had a curfew since 1910, Abdollahi said. But it was last updated in 1958 and hasn't been enforceable since 2002. The city's rule became invalid after a state law changed as a result of a court case that said curfews had to include certain exceptions for teens like waiting for a bus. The ordinance would meet the conditions of the new state rules, she said.

Enforceability doesn't mean that the curfews work, though, critics say.

A 1998 Center on Juvenile and Criminal Justice report finds that juvenile curfews in California have not reduced youth crime. In some cases, curfew enforcement actually resulted in higher juvenile crime rates, according to the report. Applying the curfew generally translated into higher misdemeanor arrest rates.

The San Mateo ordinance would result in an "infraction" for those cited, said Abdollahi, which is the equivalent of a speeding ticket. Multiple citations would eventually become misdemeanor charges, she added.

"Based on the current evidence, a crime reduction strategy founded solely on law enforcement intervention had little effect and suggests that solutions are more complex," according to the report.

The San Mateo City Council meets at 7 p.m. Tuesday at City Hall, 330 W. 20th Ave.