HELENA, Mont. (AP) _ The state Supreme Court has thrown out Montana's ``reasonable and proper'' daytime speed limit, a decision that some fear could turn highways into racetracks.

In a 4-3 ruling Wednesday, the court said the law was unconstitutionally vague and did not give drivers fair notice of what specific speed is fast enough to be a violation.

Col. Craig Reap, chief of the Highway Patrol, said he is worried that the ruling will encourage some motorists to drive at breakneck speed as the busy holiday period begins.

``There will be some that think there is absolutely no control,'' he said.

Montana's current nighttime speed limits are 65 mph on interstates and 55 mph on two-lane highways, and those are not affected by the court's ruling.

State officials quickly vowed to get another speed limit on the books.

``I think we need to get a speed limit imposed in this state as soon as reasonably possible. This is a serious situation,'' said Attorney General Joe Mazurek.

Montana is the only state without a numeric daytime speed limit for cars and light trucks. The previous law, referred to as the ``basic law,'' has been on the books for more than 40 years.

It was supplanted by the federal speed limit during the 1970s, but became Montana's only general speed law again after Congress repealed the federal limit in December 1995.

The law required that motorists drive no faster than is reasonable and proper for conditions, such as traffic, weather, and road surface.

Police officers could rely on other laws, covering reckless and careless driving, to control the fastest speeders. However, conviction under those laws requires evidence of a disregard for the safety of people or property.

Legislative leaders have predicted certain passage of a law to restore posted limits. Mazurek and Gov. Marc Racicot are backing a proposal that would affect both day and night speed limits.

Under the plan, the maximum speed on interstate highways would be 75 mph day and night. The limits on two-lane roads would be 70 mph in daytime and 65 at night.