For a growing number of motorists getting new tires on their cars, there's something waiting in the trunk: their old tires.

The alternative can be a charge of a dollar or more for "tire disposal."

As environmental concerns compound the difficulty of disposing of old tires, dealers increasingly are shifting the burden -- or the cost -- of disposal to their customers.

Each year, Americans add 279 million used tires to the 2.5 billion to 3 billion already stockpiled for disposal. And tires present a unique disposal problem. Buried, they have a disconcerting habit of bubbling to the surface within a few years. "Like vampires, used tires don't stay buried in their grave," said Rep. Esteban Torres (D-Calif.), who has introduced a bill designed to promote recycling.

Stockpiled above ground, they are a fire hazard because of their high oil content. A mountain of 9 million tires in Winchester, Va., burned for the better part of a year before dying out in 1984, causing the Environmental Protection Agency to spend $1.3 million collecting the oil runoff. Maryland's Environmental Services Agency is cleaning up a mound of 2 million tires left behind in Hughesville by a tire processing company that went bankrupt.

"They're a nuisance," said Tom Benedick, national service director for NTW Inc., one of the Washington area's largest tire dealers. In the Washington area, NTW pays a tire processing company to haul away old tires. The processor, Emanuel Tires, takes away about 51,000 tires a month from NTW's 17 local stores and disposes of them in a number of ways.

Stidham Tire Co. gives customers their choice of taking the tires or paying $1.50 to dispose of them. "That's what it costs me for the people who come haul them out of here," said Dan Lavely, manager of a dealership on P Street NW.

"No one buys tires," said Mary Sikora, president or the Recycling Research Institute, a company that tracks what happens to old tires. "They're still a disposal problem rather than ... treated as a resource or a feedstock."

In the past, tires were retreaded and reused, but cheaper radial tires have all but eliminated the market for retreads, according to Benedick. Landfills increasingly are refusing to take tires, and many of the nation's landfills are closing anyway, increasing the pressure to come up with an alternative disposal method.

"What is being done, frankly, is that as much as 70 to 75 percent of them are being stockpiled," said John Serumgard, vice president of the tire division of the Rubber Manufacturers Association, a trade group.

Tires also are being ground up and used as an additive in asphalt, but there are technical problems with the process, Serumgard said. Some are recapped and exported or used on trucks or farm vehicles. Others are bound together and used as floating breakwaters or fishing reefs, but that takes care of only a tiny percentage.

Goodyear Tire & Rubber Co. has invested in a company called Waste Recovery Inc., which collects and processes some of the tires from Goodyear-owned stores. The so-far unprofitable company operates facilities in Portland, Ore., Houston and Atlanta that chop up tires and sell them to cement manufacturers and paper mills.

The tire chips, which have a high heat value, help offset moisture when they are added to the wood waste used for fuel. Electric power plants also may eventually be able to used ground tires as a fuel additive.