HELENA, Mont. — In big, wide-open Montana, a state trooper might have to drive more than 100 miles to answer an emergency call, and routinely puts several hundred miles on the odometer in a day.

With gasoline at $4 a gallon, all that driving is tearing up the Highway Patrol's budget.

It is the same story elsewhere around the country, especially in big, sparsely populated Western states with vast stretches of highway. State police agencies nationwide are scrambling to reduce gasoline use and find the money to cover their costs. Some are beginning to worry that they will have to cut back on hiring officers.

For the Highway Patrol in Montana — the fourth-largest state in area, at 147,000 square miles — the options are limited.

The Highway Patrol considered buying more V6 Chevrolet Impala cruisers to save gasoline, but initial tests showed the Impalas get about the same mileage as the department's V8 Ford Crown Victorias, or a little more than 15 miles per gallon.

Switching to hybrid vehicles is out of the question, since there is no hope of chasing down bad guys in one, police say.

"They're gutless," said the head of the Highway Patrol, Col. Paul Grimstad, who oversees about 200 state troopers and owns a hybrid. "The one I have gets awesome gas mileage and runs good. But if you floor the thing, it doesn't have the performance. Not even close."

That has left him looking at the possibility of buying motorcycles. But Montana's harsh winter would prevent year-round use.

The Highway Patrol is over budget more than $340,000 in gas costs alone. To help cover its expenses, the agency has dipped into its personnel budget. It has yet to delay the hiring of officers, but that is a possibility if gas prices remain high, Grimstad said.

"It will have a domino effect," he said.

State police do a lot more driving than city police, and gas is a much larger part of their budgets. In some cities, police can patrol by bike or on foot — an option not available to state troopers.

New Mexico, the fifth-largest state in area, is expected to address the issue at a legislative session in January.

"We've got such a big state and lots of miles to cover," said New Mexico State Police Lt. Rick Anglada. "We have asked officers to shop around and know where the cheapest gas is to buy."

Officers in New Mexico are also being asked to car pool if they know they are traveling to the same place, such as a training meeting.

The Nevada Highway Patrol, about $1 million over budget on gas, is getting officers to drive less.

"I see more troopers than I did before — sitting under bridges, on on-ramps, using their radar," said spokesman Dan Burns. "We are trying to save gas and it is actually working quite well."

The agency is also keeping cars in service longer to save money, using them for up to 105,000 miles instead of replacing them at 80,000 miles.

The California Highway Patrol planned ahead and bought much of its gasoline at lower prices some time ago under long-term contracts. It also set aside money in case of price increases. The agency said it does not expect any budget problems.

"We don't feel that we can change our patrols or mission. We just have to be out there," said spokesman Tom Marshall. "We have to handle the crashes and be there as a deterrent."

Ron Ruecker, president of the International Association of Chiefs of Police, said there is only so much the agencies can do to save money. State legislatures will ultimately have to fork over more money for gas, or see fewer patrolmen on the road, he said.