They sneak up in pickup trucks, station wagons and two-door sedans. Some come barehanded. Most are armed with axes and saws. And all have larceny in their wood-burning hearts.

"We have been wrestling with it for three or four years and it just gets worse," says one of the half dozen rangers assigned to protect the one million acres of Virginia's George Washington National Forest from wood-hungry homeowners who see firewood where the forest service sees trees. "The energy situation," says the ranger, "has created all kinds of problems for us."

The demand for wood as a home heating alternative has created a budding market for both firewood and stoves to burn it in. It has also spawned a new category of thief -- the wood rustler. And he's proving to be as elusive in the Washington area woodlands as the cattle rustler was in the wild,wild west.

"Once a tree is out of the woods it's pretty hard to make a positive identification of it," says Cpl. John Hoback of the Prince William County Police Department. "One oak looks pretty much like another. Not too many people stencil names on their trees."

Area police do not have statistics on wood crooks because those arrests are lumped with more general larceny categories. But law enforcement officials concede that there have been few arrests. By the time they get to the scene of a crime all that usually remains is splinters.

"Most folks just don't consider it a real crime," says George Berklacy, a spokesman for the National Park Service which supervises 76 million acres of parkland, including the woods along Virginia's George Washington Parkway and the District's Rock Creek Park. Yet, as Berklacy says, "Taking a tree or even a limb from a National Park carries a maximum penalty of $500 and six months in jail."

Because Rock Creek Park, for instance, is a back yard for thousands of Washington residents, the temptation to take wood is often indulged, said Berklacy. Park rangers regularly find picnickers loading twigs and dead limbs into car trunks. The amateurs are usually let go, says Berklacy, "after some discreet butt chewing."

But not all wood thieves are amateurs. Prince William police are still looking for the poachers who last fall made off with trees worth thousands of dollars for their furniture-quality wood from a Dale City site.

"Everybody isn't cutting wood to burn. there are some very sophisticated thieves who know the value of certain kinds of wood," says Charles F. Finley, the executive director of the Virginia Forestry Association, a private organization of 1,500 woodland owners.

Finley, who has had trees stolen from his own land near Richmond, concedes there is not much that can be done after the cutting and hauling have been done.

"I'd feel sort of silly walking into the sheriff's office trying to describe my stolen property," says Finley. "Let's see, it was big, had brown bark and didn't make a lot of noise."

Law enforcement officials say that most of the illegal wood cutting is done by individual homeowners looking to save money on heating bills. Because the cost of commercially cut wood has increased so radically in the last few years, city folk are taking power saws into their own hands and heading into the forest.

A cord of wood, which is measured as a stack four feet wide, four feet high and eight feet long, is being sold in the metropolitan area this year for an average price of $105, about double the price of four years ago. Air tight wood stoves sell for between $100 and $800. And local merchants say they're selling.

"I'd say our volume this year is about 20 times what it was in 1971," says Jerry Taylor, one of the owners of Acme Stove Co. in the District, which has been selling wood stoves for 48 years.

"There are about 4,000 manufacturers [of stoves] now," says Taylor who moans that wood stoves are being sold everywhere from supermarkets to sandwich shops. "I have seen stoves for sale in a barber shop in Frederick," he says.

There are a few places wood hunters can legally cut wood. The Maryland State Forest in Cedarville this year issued free wood-cutting permits for 30 acres of the 3,000 acre forest. But the cutting season lasted just two months and ended in November.

Virginia's George Washington National Forest, located in the Blue Ridge Mountains, also issues permits to cut and haul dead wood. But ranger John Coleman warns that the cost in time, energy and gas to scavenge a limited section of the forest 75 miles from Washington often is more than the cost of commercially cut wood. And when you buy wood already cut, says Coleman, you are in danger of nothing worse than splinters.

"We have had several incidents where one cutter felled a tree on another cutter's truck," says Coleman. The number of wood-cutting permit requests for the George Washington forest has incrased from 500 to 5,000 in the last few years, he says. "It's crazy. It's contagious."

The Consumer Product Safety Commission reports that for the first six months of 1980 there were 42,000 wood-cutting injuries treated in hospital emergency rooms. There was no figure on how many of those injuries resulted in death.

"People who don't know how to use chain saws can get in a lot of trouble with them," says Coleman. "That thing will eat you up and it won't quit."

People who cut wood illegally soon will have an added element to worry about. Area police and park rangers say the problem of poaching has gotten bad enough to warrant stricter enforcement of laws.

"We've had enough complaints; if we catch you, we're going to prosecute you," said a Prince William officer, who then added his own personal assurance. "I've got five cords of wood around my house and if someone touches any of that, they'll be stuck on my fence in the morning."