GEORGE WASHINGTON NATIONAL FOREST,VA. -- Joyce Kilmer was wrong. God isn't the only one who can make a tree. Glen Thomas can do it, too -- if you give him the right pieces.

Searching for evidence that could link two Virginia men to the illegal cutting of trees in the George Washington National Forest, Thomas, a special agent with the U.S. Forest Service, rummaged through stacks of wood on their property. For hours, he patiently matched split logs until he had pieced eight trees together. Then he photographed their "butt cuts," the point where they had been severed from their stumps.

Photographs in hand, he returned to the forest, looking for newly sawed stumps with matching cuts.

"Sure enough, we found eight butt cuts that seemed to match up, so we cut those stumps down a bit further and brought 'em back," Thomas said.

The result was a positive match, and a date in court for the two men.

It was all in a day's work for the 39-year-old Thomas, whose job is to track down illegal activity in the 1.1-million-acre George Washington National Forest, which stretches nearly half the length of Virginia, from just outside Front Royal in the north to near Roanoke and Lexington in the south, where it merges with the Jefferson National Forest.

Thomas, a 15-year member of the Forest Service, is the sole full-time law enforcement agent in the George Washington Forest, a job that keeps him pretty busy.

In 1984, 604 illegal incidents were reported in his forest; last year the number more than doubled, to 1,223.

The crimes, most of which go unsolved, range from shooting up Smokey the Bear signs to stealing black cherry timber, and the increase is being felt nationwide. Forest Service personnel said there were reports of 41,500 criminal incidents in the nation's 156 national forests in 1984, and 47,600 last year.

"Our major problems . . . are near the major metropolitan areas," said Jay Humphreys, a Forest Service spokesman. Humphreys attributed the increase to improved reporting techniques and the rising number of people using the forests.

Although many people confuse the national forests with the more familiar national parks -- which one Forest Service official described as having "the crown jewels: Yellowstone, Yosemite" -- each year twice as many people visit the forests, which cover 191 million acres from Alaska to Puerto Rico.

In 1986, the Forest Service counted 225 million "visitor days" -- a camper staying five days counts as five visitor days -- up about 26 million from a decade earlier. Last year, the George Washington Forest recorded 1.7 million visitor days.

In addition to increased visits, other factors cited as contributing to the increase in reported crime include new regulations -- for example, rules governing the use of increasingly popular four-wheel-drive vehicles -- and rising prices for timber and marijuana, which can be found growing side by side in the forest.

In California, a pound of high-quality marijuana can fetch $5,000, said Ed Feu, assistant branch chief for law enforcement for the Forest Service. Not coincidentally, he said, the Forest Service confiscated 226,000 marijuana plants last year, compared with 58,000 plants in 1984.

Currently, Glen Thomas and his infrared sensors are keeping watch over four major marijuana gardens.

"The forests are ideal" for them, he said. "They're in nobody's back yard, so even if you find the plants, you don't know whose they are unless you catch someone working them . . . . We are finding that they are smaller now, to avoid aerial detection."

But while drugs are the leading problem in many southern and western forests, in Virginia timber theft takes the honors.

The going price for a cord of firewood around Washington is about $150 today, higher even than during the energy crisis of the mid-1970s, according to Forest Service officials.

"Even though you can get free permits to collect dead or down timber, some people go to areas where they aren't allowed and cut down trees for firewood," said Terry Lewis, public affairs officer for the George Washington Forest.

Forestry specialists say the demand for wood has risen 70 percent nationally in the last 30 years, in large part because of a booming paper industry. As the demand has increased, so have prices. A single log of top-quality black walnut or other fine hardwoods can sell for thousands of dollars, foresters say.

The George Washington Forest is 83 percent hardwood, officials say.

The men Thomas arrested, C. Thomas Lotts and Walter W. Ramsey, both of Staunton, were charged in June with three felony counts of theft and conspiracy. If convicted, each faces a maximum of $250,000 in fines and 10 years in prison.

"We're alleging they were in the firewood business," Thomas said.

Keeping an eye on a million acres isn't easy, so Thomas relies on tips from visitors, campers and loggers. It was such a tip last spring that led him to Lotts and Ramsey, he said.

Acting on the information, Thomas dressed in camouflage fatigues, went to the designated site and waited. As he watched from behind an oak tree, the two men pulled up in a pickup truck and took out a chain saw, he said. As they cut a 50-foot white oak to its knees, Thomas took their pictures, then pulled out his badge and arrested them.

After the two were released on bond, Thomas drove them home. "They said, 'Hey, that's awfully nice of you to bring us home.' Then I showed them the warrant {to search their property} and said, 'Don't worry about it. I was going there anyway.' "

Along with the matching butt cuts, Thomas said he plans to submit as evidence fingerprints taken from beer cans discarded near the stumps, a broken truck mirror found nearby and perhaps the men's chain saws and axes.

"Like a blind date, you never know how one of these investigations is going to turn out," he said. "But this one looks pretty good."