Montana's week-long war against wildfire neared an end today as officials declared 10 major fires under control and decided to let three others in remote areas burn on until snowfalls douse them.

Firefighting crews from seven western states packed their muddy gear and headed home while National Guardsmen and state prison inmates mobilized to fight the range and forest fires were told the work was almost done.

The rains that gave firefighters a major boost Friday turned into a problem themselves today as mud slides blocked a few country roads and took out at least one bridge north of Helena.

"A fire that hot leaves a hard layer of ash on the hillside," said Danny Hart, a Helena National Forest ranger. "So when the rain comes, that water and mud run down like sliding on a strip of wet plastic."

The biggest of the 20 or so fires that ravaged Montana this week, the Hawk Creek fire north of Billings, was officially declared "controlled" tonight after scorching 140,000 acres of prairie and forest.

By comparison, a 140,000-acre fire centered in downtown Washington would destroy everything to a point five miles beyond the Capital Beltway.

Three fires in northwestern of Montana had still not been contained today. But since they are remote from human habitation and difficult for firefighters to reach, Forest Service officials tentatively agreed to let them burn. They will presumably keep going until the first big snow falls about a month from now.

"We're talking about a matter of weeks," said E.M. (Sonny) Stiger, a Forest Service officer in Helena. "But when you consider the danger of putting firefighting crews into that steep terrain, and the cost, and the impact on the wilderness areas, we decided the best thing to do was let it burn."

Using a computerized model of the terrain and expected weather conditions, Forest Service planners have predicted the likely path of the three fires over the next few weeks. If any starts to grow too rapidly, "smoke jumper" paratroopers will be sent in to try to regain control.

Range and forest fires are standard fare each summer in this parched and largely uninhabitated territory. But this week's conflagration went far beyond the normal summer burn.

Unusually hot days and gusty winds whipped the scattered fires into major blazes that defied the normal constraints imposed by nature. One range fire borne by driving winds leaped the quarter-mile-wide Missouri River on Tuesday.

In all, the fires this week scorched about a quarter-million acres of Big Sky Country, including scenic forests near Glacier National Park along the Canadian border. That area is about six times the size of the District of Columbia.

But because so much of Montana is essentially empty, in human terms, the loss to people was relatively small. A few firefighters were injured battling the blazes.