California motorcyclists who defy the mandatory helmet law that takes effect at midnight tonight may be issued a ticket for a moving violation or get off with a warning--depending on which law enforcement agency gets to the violator first.

The California Highway Patrol said Monday that despite earlier reports to the contrary, it will not provide the 90-day grace period that routinely accompanies many new traffic laws and will begin issuing citations at one minute after midnight.

But the Los Angeles Police Department and the Los Angeles County Sheriff's Department have said they will provide a grace period during which helmetless motorcyclists or their passengers will get only a warning. The Sheriff's Department will observe a 15-day grace period, while Los Angeles police will allow 30 days.

For motorcyclists, the issue of when enforcement begins only adds confusion to a law that has generated years of controversy.

Motorcyclists said they have heard reports for months that all law enforcement agencies would provide a grace period.

Keith Ball, editor of Easy Rider, a widely circulated magazine aimed at "lifestyle" motorcyclists least likely to wear helmets voluntarily, said his Agoura Hills-based magazine recently published an article quoting CHP spokespersons who said they would provide a grace period.

"I think it depends on who you talk to and the time of day," said Ball, a longtime motorcycle rider who plans to begin wearing a helmet when the law goes into effect Wednesday.

A first offense will cost motorcyclists $100, a second $200 and a third $250. The tickets will not, however, count as points that lead to suspension of a motorist's driver's license, said Officer Al Michel, a spokesman for the CHP's Los Angeles County headquarters in Glendale.

Michel said, however, that the CHP has maintained all along that it would provide no grace period in enforcement of the helmet law. He said the law has generated enough publicity and widespread media attention that a grace period is unwarranted.

"At this time, it is hard to find anyone who doesn't know about the law, especially motorcyclists," he said.

He said most law enforcement agencies normally provide a 30- or 90-day grace period to allow enough time to educate the public on a new law. Michel acknowledged that there may be some confusion among motorcyclists who expect a grace period for the helmet law.