The Greenbriar in West Virginia has its own gasoline pump and so does the Whip-poor-will Motel near Bristol, N.H. But the problem is getting there - or to any of your vacation destinations. So why not use some of the gasoline hot lines recently installed?

Let's say you can't decide whether to try to drive the family car up to the summer cottage on the shore. You can call Holiday Inn's new gas information number, 800 - 238-8000, and they'll not only make your reservation but give you the latest information on gas availability in the area. Each field unit manager must feed gas information about his area into the Holiday Inn computer in Memphis at least once daily. The new number has been in service only a short time, but last week operators handled four times as many calls as in the week before.

You could also call Howard Johnson's gasoline information number, 800 - 654-2000. Instead of direct information, this number will give you the number of the local American Automobile Club and the 800 - 8748660, and find the gas availability on major highways like I-75 and I-95 leading into Florida. To find such numbers for your vacation state, dial 800 - 555-1212.

Keeping gas hot lines current is a major difficulty requiring constant feed-in. Quality Inns, with 500 units around the country, is investigation the possibility of installing a line but , according to marketing vice president Bruce Cameron, the difficulty is the lack of a central clearing house. Information garnered from various state departments of energy grows old very quickly.

Best Western, the chain with the largest number of properties around the United States, wants to get the message to motorists that there is gasoline in isolated places and the trouble is apt to be urban, with New York City and Washington especially hurting. "Don't cancel your travel plans," says Wendy Black, spokesman for Best Western. "Call our reservations and gas information number to find how the situation is where you want to go." Volume on the number, 800 - 528-1234, was up 39 percent recently.

Busch Gardens, Eilliamsburg, which was Virginia's No. 1 tourist attraction last year, and Colonial Williamsburg have worked out a way to reassure motorists who worry about being able to get gasoline when they arrive. Fifty to 75 percent of the area's gasoline dealers have agreed to remain open every weekend, says Lee Williams of the Williamsburg Retail Gasoline Dealers Association, and the Williamsburg Hotel/Motel Association has installed a hot line for information about gasoline availability. In Virginia phone 800 - 582-8977, out of state 800 - 446-9244.

"We are aggressively taking our message, 'We have gasoline available' to the public," says Patrick D. Cartwright, general manager of Old Country at Busch Gardens. Old Country and Williamsburg will be broadcasting up-to-the-minute information with frequent radio spots.

At Kings Dominion, Doswell, Va. (20 miles north of Richmond), officials are "encouraging staggered hours of operation of area gasoline stations" and have erected a "gasoline availability board" in the amusement park to show which nearby stations are open. Special weekend car rental rates are being arranged, a spokesman said, Greyhound and Trailways offer bus service, and Amtrak has a one-day group tour from Washington or Baltimore.

Kings Dominion has also set up a hot line for gas reports. In the Washington area call 296-8834 or 8835.

In Hershey, Pa., "Chocolate Town U.S.A." says, "We're closer than you think" (125 miles, 6.25 gallons from Washington, they estimate), and they've also set up a gas line (not toll free): 717-534-3005. The operators of Hersheypark, Chocolate World and other attractions, are offering a free "Chocolate Shuttle" bus on their grounds so visitors can park their cars and save gas.

Most of the chains report that business nationwide is holding up because of urban units served by airplanes and trains. Best Western says that even with three out of four customers arriving by car, the occupancy rate, while down from expectations, is up from last year. Black attributes empty rooms to "media hype," since rooms are going begging where there is actually plenty of gasoline. Bruce Cameron of Quality Inns says people are getting off the road earlier and this possibly leads to an extra night away from home and good restaurant business.

Kim Mills of the American Hotel and Motel Association says she thinks a lot of families may not be planning to travel by car this summer and everybody in the travel industry is nervous.

"We think they'll travel, but shorter distances by cars," says Mills. New York City especially is trying to attract suburbanities on the weekend, and the Rye Town Hilton in Port Chester, N.Y., has a new slogan - "A gallon and a half from NYC is far as you need to go."

Vivian Conly, a spokeswoman for the Greenbriar, says if the customers can get there, they can fill their tanks in West Virginia. "We've read about the trouble," she says, "but it's like we're on another planet."

Robert Moran, vice president for corporate affairs for Phoenix-based Ramada Inns, which has 610 units mostly in the South, Southeast and West, says his wife just drove across the country and had no trouble until she got to Washington. On the other hand, a man he was talking to on the phone on New York hung up abruptly because he had spotted a short gas line outside the window.

Many of the resort spots are trying to work out their own problems.New Hamshire has put in a state hot line, 603 - 224-2525, manned by the Office of Vacation Travel, which routes and advises prospective visitors. The Pocono Mountains Vacation Bureau in Stroudsburg, Pa., is manning a gasoline hot line number, 717 - 629-1900, and so many people are dialing that it's hard to get through.

What do the travel people see ahead this summer?

"I think we will see an adjustment of travel patterns," says Charles Barnette of Holiday Inns, "fewer weekend jaunts but - with caution - people will get where they want to go."