DENVER -- U.S. military troops are being called in to help firefighters battle blazes across the West, in what's being called the worst U.S. forest fire season since 1996.

Fires are charring tens of thousands of acres in more than 70 separate blazes scattered across 10 Western states, where weather forecasts are calling for more hot and dry conditions.

In Colorado's Mesa Verde National Park, crews were making progress containing a fire that has burned 22,600 acres and threatened the nation's largest archeological preserve.

The park is home to 18 ancestral cliff dwellings that have links to 24 American Indian tribes scattered throughout the Southwest, according to the National Park Service.

Although 40 percent of the fire was reported contained Wednesday, evening thunderstorms and limited access to "hot spots" hampered some firefighters, according to the National Interagency Fire Center Web site.

'Already resources are thin'.

"Here we are approaching the end of July and already resources are thin," said Amy Teegarden, a spokeswoman for the U.S. Forest Service in Helena, Montana, where two fires have destroyed more than 23,000 acres.

"We're just now getting into what is normally the busy fire season," she said.

U.S. Forest Service spokesman Dave Turner said the fires near Canyon Ferry Lake, Montana, east of Helena, were expected to burn on Thursday, spewing smoke into the Helena Valley.

"We're just glad they saved the house because we had about 15 minutes to get out of there, and when we left we saw a wall of flames," said Gen Pedersen, who was among the first evacuees when the fires began Sunday.

Dozens of families have been evacuated from scattered small ranches in the region, and residents of two personal care facilities for the elderly also were evacuated.

U.S. asks Canada for help

Elite firefighting crews, air tankers and helicopters are in demand because of the widespread wildfires. Federal authorities have asked Canada to send firefighting planes. They also have asked Montana Gov. Marc Racicot to encourage businesses and state agencies to let employees volunteer for fire duty.

Overall, about 5,600 federal firefighters were on duty on Wednesday, in addition to crews from state and local agencies. Personnel have been recruited from Maine, New Hampshire, Pennsylvania, Connecticut and Georgia.

Other states battling wildfires were Arizona, California, Idaho, Nevada, New Mexico, Texas, Utah and Washington.

Soldiers to join crews next week

In hopes of gaining ground on the fires, Army soldiers will attend crash firefighting courses organized by the National Interagency Fire Center in Boise, Idaho. Center spokeswoman Lorraine Buck said the soldiers should be ready to join fire lines next week.

It will be the first time soldiers have been called into help U.S. firefighters since 1996, when 1,160 troops helped battle fires that burned 3 million acres by July 25.

So far this year fires have burned 2.6 million acres. Buck said she did not know how many soldiers would have to be called in.

The 2000 wildfire season began to gain national attention in May, when a devastating blaze raged out of control and destroyed more than 200 homes in Los Alamos, New Mexico, threatening the Los Alamos National Laboratory.

The long-range forecast for Western states calls for much more hot, dry weather before the season ends.