* Governor calls it Colorado's worst fire season
* Obama plans to visit state later this week
* Western states battling 35 large wildfires (Updates evacuation figures, details; still no damage toll)
By Keith Coffman
COLORADO SPRINGS, Colo., June 27 (Reuters) - Firefighters struggled on Wednesday to beat back a fiercely aggressive wildfire raging at the edge of Colorado Springs that has forced at least 35 , 000 people from their homes and was nipping at the edges of the U.S. Air Force Academy.
The so-called Waldo Canyon Fire, fanned by gusting winds, has gutted an unknown number of homes on the wooded fringes of Colorado's second-most populous city and prompted more evacuations as flames roared out of control for a fifth day.
President Barack Obama plans to pay a visit to the area on Friday to view the damage, the White House said.
The blaze flared Tuesday night with sudden ferocity and quickly overran fire containment lines, invading the northwestern corner of the city. But officials have declined to characterize the extent of property damage there.
Colorado Springs Fire Chief Rich Brown told Reuters that he had "a number in mind" for the approximate tally of homes lost in Tuesday night's firestorm but did not want to release that information until residents of those dwellings were notified.
The blaze left an orange hue over Colorado Springs, and a smoky haze hung in the air, so thick in places that the giant, roiling pall of smoke that continued to billow into the sky over the city was obscured from the ground.
Governor John Hickenlooper said after flying over the fire zone Tuesday night that he saw many homes destroyed in a "surreal," luminous landscape below, but did not give a number.
Pressed for an estimate of property losses on Wednesday, fire information officer Greg Heule said, "We've started the process of identifying the structures, but we haven't completed the inventory," adding "there's still active fire in there."
Brown called the firestorm threatening his city - in a metropolitan area of more than 650,000 people - "a monster" and said that flames were "not even remotely close to being contained."
The fire, which has scorched more than 15,000 acres (6,070 hectares) in the shadow of the famed Pikes Peak mountaintop, was not as intense early on Wednesday as the day before. But thunderstorms hampered firefighting efforts by bringing erratic winds, whipping flames from one direction to another.
"I've never seen any progression like that," incident commander Rich Harvey said at a late-afternoon news conference. "The winds keep shifting on us. Again the winds are causing us problems out here."
The number of evacuees stood at 32,000 on Tuesday night. But after additional residents in and around the nearby town of Woodland Park, population 7,600, were ordered from their homes on Wednesday, El Paso County Sheriff Terry Maketa said the number displaced people had grown by about 3,000.
Colorado wildfires have killed four people so far this year in what the governor called "the worst fire season in the history of Colorado," but no serious injuries from the Waldo Fire were reported on Wednesday.
AIR FORCE SENDS HELP
The Air Force Academy said the evacuation zone included two communities of single-family homes on its grounds housing around 2,100 civilian and military personnel and their families. Despite the blaze, the academy will welcome a class of over 1,000 new cadets on Thursday, officials said.
Proximity to the academy, which saw a spot fire break out on its grounds in one vacant corner, seemed to bode well for U.S. government support in responding to the emergency.
The Air Force said it was dispatching up to 25 military helicopters, joining four giant C-130 air tankers already devoted to the effort. Over half of federal firefighting resources are deployed in Colorado, the White House said.
Fire commanders said they have called for reinforcements and expect to have as many as 1,000 personnel on the lines soon.
At a gas station in Colorado Springs, Andrew Heintzelman, 34, said he had been on the roof of his home in the nearby community of Mountain Shadows on Tuesday trying to keep the flames at bay but had since been forced to flee.
"I was spraying the hose on the shingles and the cops came through the neighborhood and told me to get out now," said Heintzelman, 34, who lives with his mother.
Animal welfare groups said shelters had taken in scores of dogs, cats and even a turtle and pet rats displaced by the fire. Of particular concern to veterinarians was the risk that horses could suffer colic from being moved too quickly and that pets were being spooked by the steady wail of sirens.
The Waldo Canyon Fire was one of about a dozen burning across Colorado. The biggest of those, the High Park fire near Fort Collins in the northern part of the state, has consumed 87,250 acres (35,300 ha) but was 65 percent contained. It now ranks as the most destructive wildfire on record in Colorado after devouring about 250 homes.
Elsewhere across the Rocky Mountain West, a wildfire in Montana that has scorched 19,000 acres (7,690 ha) in the eastern part of the state has forced 600 residents to leave their homes, said Kent Atwood, a state hazard mitigation officer. An unknown number of houses were destroyed in Montana.
In Utah, authorities found a body in the ashes of the fast-moving Wood Hollow Fire about 100 miles (160 km) south of Salt Lake City on Tuesday, marking the first fatality in a blaze that has scorched more than 46,190 acres (18,692 ha) of rolling hills covered by parched cheatgrass and sagebrush.
Colorado accounts for eight of 35 large, active wildfires being fought across the country. The bulk of them were in nine western states - Colorado, Montana, Utah, Wyoming, South Dakota, New Mexico, Nevada, Arizona and California - according to the National Interagency Fire Center in Boise, Idaho.
Although federal authorities say the fire season got off to an early start in parts of the northern Rockies, the number of fires and acreage burned nationwide is still below the 10-year average for this time of year, according to fire agency records. (Additional reporting by Ellen Miller in Grand Junction, Jennifer Dobner in Salt Lake City and Laura Zuckerman in Salmon, Idaho; Writing by Steve Gorman and Alex Dobuzinskis; Editing by Cynthia Johnston and Eric Walsh)