Firefighters widened a defensive ring around a mountaintop observatory Monday, trying to hold back two wildfires and protect a powerful telescope under construction.

The crews in southeastern Arizona used bulldozers and fire retardant around the Mount Graham International Observatory (search), which has two operating telescopes and the $120 million soon-to-be-completed Large Binocular Telescope (search). The ground crews were helped by an air tanker plane dropping retardant.

"The building's not going to burn, but the smoke and heat could do some real damage to the instruments inside," said Pruett Small, a fire official.

Researchers from around the world use the observatory, which is an extension of the University of Arizona. When fully operational in 2005, the Large Binocular Telescope will be the world's most technologically advanced optical telescope. It's expected to yield images nearly 10 times sharper than those from the Hubble Space Telescope (search).

The observatory, consisting of eight buildings, encompasses 81/2 acres of pine forest on Mount Graham's 10,470-foot Emerald Peak and is surrounded by a 200-foot-wide clearing. It also has a sprinkler system that officials said would be turned on if flames came within a quarter-mile.

One of the two threatening fires was a lightning-sparked blaze that had grown to more than 6,200 acres by Monday. It was burning less than a mile southeast of the $200 million-plus observatory.

A nearby blaze that had grown to more than 6,500 acres prompted the evacuation of the observatory and 85 cabins on the mountain Friday. That fire was about 3 miles northwest of the observatory.

"I can't hardly stand it to think there's a fire up there," said Verna Colvin, whose family owns a cabin in Turkey Flat. "It won't be the same if it burns up. It's like my life is going."

In central Arizona, the threat posed to the city of Payson by an 84,300-acre wildfire eased after crews reinforced their fire lines near the forest community.

The U.S. Forest Service also sent a tanker plane to help with that blaze. The planes, former Navy P-3 Orions, arrived in Arizona on Sunday, two days after federal officials said the aircraft's private operator had demonstrated they are safe to fly, said Ken Frederick, a fire information officer.

In Alaska, an evacuation order remained in effect for 277 homes and businesses threatened by a blaze some 30 miles north of Fairbanks that had spread across 307,000 acres. The blaze began to die down somewhat Monday, with help from light rain and high humidity.

Similar conditions aided firefighters battling a 200,000-acre fire about 50 miles northeast of Fairbanks.

There are 62 active fires in Alaska. So far this year, wildfires have burned more than 1.8 million acres in the state.

In central Washington, two fires near Lake Chelan have burned a total of nearly 5,500 acres. There were no reports of structure damage or serious injuries. Hundreds of firefighters were trying to make headway against the two fires before expected high winds later in the week. Helicopters scooped water from the Columbia River and Lake Chelan to drop on hot spots.