Federal and local officials expressed fear today that unexpected severely dry weather throughout the western states may mean that runaway fires this week are only the beginning of a summer of historic devastation.

The main problems, officials said, have been high temperatures, low humidity and an early and smaller-than-expected runoff of mountain snow. They also cited budget cutbacks during the last four years, all relatively fire-free.

Today, fires in nine western states increased the most recent toll of destruction to more than 200,000 acres, Associated Press reported. The usual beginning of the peak fire season is still a month away.

The Boise Interagency Fire Center in Idaho reported 1.45 million acres consumed by fires nationally this year, compared with 1.28 million acres in all of 1984.

For the first time in several days, the weather helped firefighters today as winds died a bit and temperatures dropped to the 80s and 90s from the 100-degree-plus records earlier this week.

Paul Werth, a meteorologist with the Boise center, said, "Our current condition is what we would normally see in the early part of August, but now we have two to three months of dry weather coming up."

George Castillo, a spokesman for the U.S. Forest Service in Washington, said any series of major fires could stretch equipment and manpower near their limits because budget allocations for firefighting have reflected the limited requirements of the region's last few years, all wet. "The tendency is to base your budget on last year's activity," he said.

In the biggest fire this week, a 66,650-acre blaze in Los Padres National Forest east of Santa Barbara, the forest service rushed crews from as far as Michigan and Arkansas to relieve some of the 2,829 persons fighting the fire. The service also issued a radio and television appeal for civilian trucks and vans to haul supplies, at $7 an hour and as much as 35 cents a mile, and a traffic jam of volunteers resulted.

A cool coastal fog this morning helped slow that fire, fueled by brush that in some canyons has grown more than 30 feet because it escaped fire for 30 years.

Forest management experts have suggested controlled burning to limit danger in such areas and duplicate natural fires that trimmed the brush before man arrived. But such burns are difficult to arrange and involve dangers of their own.

The other large California fire still not under control is a 32,000-acre blaze in San Luis Obispo County, where 1,258 firefighters are at work.

Investigators continue to pursue evidence that the Santa Barbara area fire, and several others in southern California this week, were set by arsonists.

Arnold Hartigan, spokesman for the Boise center, said as many as 90 percent of forest and brush fires near urban areas are thought to be set by humans, either accidentally or intentionally. In uninhabited areas, he said, the principal cause is lightning.

Los Angeles fire officials have reported finding what they called "incendiary devices," apparently dropped from a car into uncut brush before Tuesday's devastating fire in the Baldwin Hills neighborhood. Three persons died, 48 houses were destroyed and more than 300 persons were left homeless there.

City officials have criticized property owners who did not cut back brush and weeds as required and have suggested that stiff fines be added to the law governing such property management.

Recent suspected arson brush fires here and in San Diego and Palo Alto have caused an estimated $31 million in damage involving more than 140 homes.

Werth, monitoring regional weather from Boise, said the problem began in December after a wet fall that had continued the pattern of good precipitation over the last three years.

"In late December, for some reason we really don't understand, the pattern changed," he said. Weather turned extremely dry, mountain snow packs did not reach their usual height and an early 1985 warm spell melted them quickly and left little water to prevent a very dry spring.

This has left the unusual situation of droughts on both ocean coasts. Los Angeles, for instance, has received less than half of the nearly 11 inches of rain it normally averages by July.

Werth said fire experts have made special note of the outbreak of forest blazes on slopes that face away from the sun and where conditions are usually cool and moist.