Fire officials said the promise of light rain Sunday could slow the advance of a 280,000-acre fire in Alaska's spruce-and-tundra interior, but they warned it wouldn't be enough to allow hundreds of residents back into their homes.

A week-old evacuation order remained in effect for 277 homes and 12 businesses threatened by the Boundary fire 30 miles north of Fairbanks. One home was damaged and the fire was 15 percent contained.

Alaska State Troopers were letting some homeowners through to retrieve possessions or check on property, said fire information spokeswoman Teresa McPherson.

"But troopers are discouraging people from staying," she said.

On Tuesday, Hundreds of people sought refuge in Fairbanks, Alaska's second-largest metropolitan area with about 82,000 residents, when the fire tripled in size.

Cooler weather Saturday helped slow down the Boundary fire and the 170,000-acre Wolf Creek fire to the east.

The Alaska Army National Guard planned to send two Blackhawk helicopters to Fairbanks on Sunday and a third aircraft and crew was on standby at Fort Richardson in Anchorage. The helicopters are equipped with 900-gallon buckets that can drop water on fires and carry crews and equipment.

The Wolf Creek fire 50 miles northeast of Fairbanks had charred 174,000 acres in a popular recreation area. Several people living in the area had voluntarily left their homes. Fire managers discovered Saturday that the fire burned five cabins Thursday.

There were 60 active fires in Alaska on Saturday; crews were fighting 10 of them and the others were being monitored. So far this year, 333 fires have burned nearly 1.7 million acres in the state.

Elsewhere, an observatory in Arizona was being threatened by a wildfire that grew to 1,800 acres on Saturday. The observatory is home to the $120 million Large Binocular Telescope -- one of the world's most powerful optical instruments, and two smaller telescopes.

The fire was burning less than a mile southeast of the $200-plus million Mount Graham International Observatory, about 110 miles northeast of Tucson.

"If the wind pushes it, it could be there in two hours," said Pruett Small, operations section chief for the team fighting the fires.

The blaze, which was caused by lightning, and another 3,500-acre fire nearby prompted the evacuation of the observatory and 70 to 80 homes on the mountain Friday. No homes or cabins were imminently threatened, officials said.

The two Arizona fires were 5 percent contained Saturday.