Like a group of red-faced children who have just learned why Mommy and Daddy said not to play with matches, some of America's top environmentalists have been burned by underestimating the primal power of fire.That lesson was brought home as Yellowstone National Park, often called the crown jewel of the park system, was being ravaged by at least a dozen wildfires - the worst devastation in the park's 112-year recorded history.

The fires this year are far worse than the worst-case scenario described in the fire management plan that park officials were using when the holocaust erupted last week.

Citing a study of natural fires over the last 200 years that burned with and without human intervention, the plan concludes: "It is evident that fires greater than 40,000 acres probably won't occur."

But at week's end, almost 110,000 acres had been consumed by a dozen fires. Just one of those blazes, the Clover-Mist Fire on the park's northeast boundary, had reached 68,000 acres.

Following longstanding policy, park managers at first let the blazes burn for ecological reasons. Environmentalists see lightning-caused fires as an essential part of the life cycle of forests, clearing away old and dead trees and making it possible for new growth to begin.

Now, however, park officials are desperately trying to contain the fires for reasons of pure survival. Three thousand men and women are at fire lines thrown up around blazes in every corner of the sprawling park.

U.S. Forest Service official Bruce Fox spoke for many firefighters when he observed that the battle is particularly hard because the blazes were allowed to grow into monsters before troops were fully committed.

The fight began in earnest only after blazes threatened to ravage some of the park's most famous features, including the Old Faithful geyser resort, and after clouds of pungent pine smoke started blackening the sky, frightening and often inconveniencing thousands of tourists.

In response to tourist complaints and protests by tourist-oriented businesses, Interior Secretary Donald Hodel made a quick trip to Yellowstone last week. He suspended the park's longstanding policy of letting most lightning-caused fires burn themselves out naturally.

Hodel praised his troops for their bravery on the lines and insisted that the "let it burn" policy is a sound management technique in most years. But it's far too dry this year to let nature take its course any longer, he conceded.

The lesson was clear: With wildfires in a tinder-dry forest like today's drought-ravaged Yellowstone, if you give Mother Nature an inch she will take mile after mile, one charred acre at a time.

The park system's 43-page manual, "The Natural Role of Fire," drawn up in 1974, explains how the heat from fire breaks open pine cones and releases seeds that are then scattered by the winds to take root with numerous other plants in the ash-enriched soil.

The fire plan concluded that "we have learned much of unhindered fire behavior in forested communities in Yellowstone Park."

But as one scientist put it as he was standing at the edge of one of the howling wildfires sweeping through Yellowstone last week, "We thought we understood fire, but we're learning lessons now that we never imagined."

John Varley, chief scientist on the park's staff, admitted in an interview that the experts had been lulled by almost 16 years of success with the "prescribed burn" policy.

Since 1974, 140 fires started and were allowed to burn with "excellent results," he said. The average fire consumed 250 acres and then simply died out. The resulting new growth proved exactly the boon to wildlife that scientists had predicted.

The problem, explained Don Despain, a botanist on the park staff, is a new, almost unheard-of weather pattern.

The park receives almost all of its moisture from the winter snowpack. Each year since 1979, Despain said, the snowpack has been below normal.

Until this year, above normal rainfall in the summers has kept extraordinary fires from starting by wetting down the overly dry trees.

"This spring we just didn't have any rain at all, and the decade of low snowpack set the stage for these unbelievably dry conditions," said Despain. While the fire plan was drafted to cope with conditions traced back nearly 200 years, Despain said, conditions now are probably the worst in 400 years.

"We share the view that a natural fire plan is very important to maintaining the ecological integrity of the Yellowstone system," said Ed Lewis, executive director of the Greater Yellowstone Coalition, an environmentalist group.

He warned, however, that the furor created by this year's freak fire season may force park managers to overreact and cancel what he considers the best plan for wildfire management. Hodel last week ordered the plan redrafted.

But Frank Rigler, a rancher in Gardiner, Mont., on the park's smoke-smudged boundary, was far less friendly. He handed Hodel a petition signed by 313 of the town's 1,000 residents demanding that the fires be put out.

"They have a silly fire plan and we are just fed up with the nonsense, with breathing their smoke," Rigler said. "You just can't mess with fire; they ought to have learned that by now."