Hoping to reduce the number of false alarms that police must answer, the Los Angeles City Council voted Wednesday to impose tougher penalties on the owners of security systems that generate false calls.

Although the measure was endorsed by police, it prompted an acrimonious, hourlong debate that ended with a 9-to-5 vote. Several council members endorsed the measure only after its backers agreed at the last minute to adopt the new penalties on a one-year trial basis.

Because the vote failed to get a 12-vote majority, it will require a second vote next week before it becomes law. However, police officials said they were not sure when they could begin to impose the new penalties.

Currently, owners of security alarm systems that generate more than four false alarms in a 12-month period face an $80 fine. The new law imposes the fine after the second false call.

In addition, owners of security alarms that are not registered with the Police Department can be charged with a misdemeanor, punishable by a fine of up to $1,000 or one year in jail, after the first false alarm. The current law only imposes a fine of $80 for owners who fail to register their systems.

Police Chief Willie L. Williams and the Police Commission have supported the tougher fines because they say they will reduce the number of false alarm calls and free up police to respond to real crime problems.

Opponents and supporters of the measure agree that false alarm calls are a drain on police resources. Nearly 95% of all alarm calls turn out to be false, triggered either by human error, faulty systems or weather conditions, police say.

Last year, the police responded to 147,000 false alarm calls, which accounted for 18% of all calls answered by police, according to officials.

"We catch burglars every day, but we would catch more if we didn't have so many false alarms," Police Lt. Charles Beck told the council. He added that if all the false alarm calls were eliminated, police would have up to 50 additional officers on the street at any moment.

But opponents of the new law say the tougher fines will only punish the owners of security alarm systems for false alarms that may have been caused by a faulty system. They argued that the measure would prompt residents and business owners to get rid of their alarm system.

"The way we are setting up this ordinance will only discourage alarm owners," said Councilman Mike Hernandez.