The Shenandoah National Park's biggest and worst fire in decades yesterday raged through thousands of acres of uninhabited wilderness near Elkton, Va., forcing closure of the southern third of Skyline Drive.

More than 300 firefighters, some from as far away as Massachusetts and Texas, battled heat and exhaustion in their efforts to contain the blaze, which started Friday night with a camper's stove accident in the Big Run Creek area and was quickly made worse by gusty winds and abnormally dry conditions.

The fire, with flames that shot as high as 60 feet, is expected to burn at least 4,000 acres before being brought under control, possibly today.

Charles Anibal, a National Park Service spokesman, said the fire poses no danger to area residents. Only one injury has been reported: A firefighter who twisted an ankle on the steep and rocky slopes.

Skyline Drive between Rte. 33 and Waynesboro has been temporarily closed to the public. Firefighters had hoped to contain the blaze to the west slope of the drive, which runs along the mountaintops. But yesterday afternoon, flames leaped the pavement between mileposts 78 and 79 and burned a half-acre area.

Anibal said the fire broke out about 7 p.m. Friday in a bowl-shaped valley fed by Big Run Creek. It spread up the sides, racing low along the ground, incinerating mountain laurel and small pines, but also scorching red oak and hickory trees.

"It goes around and all over the place," said Anibal. "It wiggles. It's like an amoeba. It varies." As of late yesterday, the fire was estimated to be 12 miles long and 1 1/2 miles wide.

The area is designated as wilderness, but Anibal said the unidentified camper is believed to have secured a backwoods permit. He said that the incident is under investigation and that he did not know whether penalties could or would be levied.

Firefighting costs are estimated to run as much as $100,000 a day, he added.

About 300 U.S. Forest Service workers, as well as those from the National Park Service and volunteers from surrounding towns, worked in shifts to battle the blaze. Although airplanes and a helicopter had been used to drop fire-retardant chemicals, mushrooming clouds of smoke eventually forced workers to abandon the flights.

Anibal said firefighting efforts were being hampered by laws that prevent the use of heavy equipment, such as bulldozers and chain saws, inside federally designated wilderness areas. "But a bulldozer would do more long-range damage to the environment in this particular case than a fire," he said.

Other obstacles included wind, which gusted up to 30 mph on Saturday, and the area's moderate drought conditions.

National Weather Service forecaster Scott Prosise yesterday had no rainfall statistics for the park but said they were likely the same as for the Washington metropolitan area, where 8.59 inches of precipitation have fallen since January; the normal level is 12.08 inches.

The fire, which as of late yesterday had consumed an estimated 3,400 acres, is thought to be the largest inside the park since the 1930s, when a series of blazes burned dry forests of dead chestnut trees, Anibal said.

The second largest occurred about 25 years ago and burned 1,300 acres, he said.