A thick whitish-blue cloud of smoke hung over the heart of the Shenandoah National Park today as firefighters scrambled for the third day to contain one of the worst Virginia forest fires in decades.

The smokehouse smell of charred underbrush permeated the mountain air over more than 4,300 acres of seared wilderness at the southern end of the forest.

Hundreds of animals fled as flames continued to hiss and crackle across the soot-black forest floor.

Most animals were able to escape the flames, which mostly destroyed brush and other low- lying vegetation rather than trees, said National Park Service spokesman Charles Anibal.

"The fire certainly is an intrusion on the natural order of this forest," said Anibal. "It will change the ecosystem for the next several years."

Park officials said that firefighters had contained the blaze within the boundaries of a 4,370-acre area by early evening today, but they warned that high winds could cause the fire to spread again.

Officials said they expect the blaze, which has been fed by gusting winds and extremely dry terrain, to continue for about a week before it burns itself out.

Two firefighters have suffered minor injuries battling the blaze, Anibal said.

The fire, which officials called one of the worst ever in the East, was started in much the same way as the half-dozen or more minor fires that break out each year at the Shenandoah National Park here.

A camper frustrated by his inability to start a portable stove Friday night tried to expedite the cooking fire by lighting a piece of paper, park officials said. The paper accidentally slipped away and began a fire in the surrounding brush.

What began as a minor skirmish for Park Service firefighters escalated into an inferno that had roared across thousands of acres by this afternoon.

"It's like fighting a war," said Charles J. Crail, a spokesman for the Park Service. "You've got the enemy approaching you on every side."

The effort to contain the fire resembled a military operation. By Saturday morning, an army of about 500 Park Service employes was rushed to the park from around the country to build a 15-mile perimeter around the burning area, park officials said.

By today they had succeeded in containing about 80 percent of the fire.

"At night . . . it looks like a volcano," said Anibal. "You can see this monstrous ring around the mountain."

Firefighters worked in groups of 20, armed with shovels, rakes and chainsaws, to build a dirt trail around the fire.

The dirt lane -- two to three feet wide -- is designed to stop the fire from spreading by depriving it of fuel.

One of the fire's boundaries is the winding Skyline Drive, which remained closed today from Elkton south to Waynesboro.

Most of the fire has been contained west of Skyline Drive, but if winds push it across the popular scenic route, thousands of acres of forest to the east will be in danger, said firefighter Tom Nash.

Fire engines and helicopters carrying huge buckets of water doused "hot spots" caused by flying sparks that ignited brush east of Skyline Drive.

Nash said he rushed to the park from his Montgomery County home after receiving a phone call Friday night.

He worked 15 hours without a break on Saturday constructing the dirt barrier, and he said he has had only 10 hours of sleep in the past three days.

"It's tough going," said Nash of the efforts to clear brush from the rugged forest on grades as steep as 70 degrees.

The fatigue felt by the firefighters was exacerbated by temperatures that rose into the 80s today.

Nash said firefighters frequently work only a few yards from the flames.

"You can hear the fire burning. It's crackling and popping," he said.

The section of the park that has been engulfed by the fire is one of the most rugged, untamed regions of the Shenandoah Mountains.

It is primarily an uninhabited wilderness area.