LOS ANGELES — Federal investigators Friday revealed conflicting accounts of why an air tanker was not summoned in the early hours of what became the largest wildfire in Los Angeles County history, but concluded it's not possible to know if different decisions would have curtailed the damage.

The 2009 Station Fire killed two firefighters, destroyed 89 homes and blackened 250 square miles on the edge of Los Angeles, and residents who were burned out have long complained the U.S. Forest Service failed to bring in enough firefighters and aircraft to halt the spreading flames.

Government records released after the blaze opened questions about whether firefighting aircraft could have been ordered and deployed more quickly, including at night, and whether a tight federal budget drove firefighting decisions on the ground.

The U.S. Government Accountability Office report concluded the Forest Service needs to clear up foggy policies that could cause confusion when working with local firefighters, but it stops short of suggesting the Station Fire could have been snuffed in its early stages.

GAO noted that firefighting decisions are made under heavy pressure with "imperfect information," and it acknowledged investigators had "only limited ability" to second-guess firefighters, given the conditions on the ground.

"Even less clear is whether, and to what extent, different decisions might have changed the outcome of the fire," the report concluded.

The report urged the agency to "clarify ambiguous operational processes" to improve how it manages future fires.

In a statement, U.S. Sen. Dianne Feinstein, D-Calif., urged the agency to clearly determine when night flights are needed and to improve how aircraft and firefighters are deployed. She lamented that "firefighters were so close to containing it on the first night."

Rep. Judy Chu, D-Calif., said "mistakes were made but there is a valuable opportunity to learn and improve" the way wildfires are managed.

The eagerly awaited study began more than a year ago, when members of Congress asked the watchdog GAO to conduct a broad review of the fire started by an arsonist in the rugged mountains that border the nation's second-largest city.

The Associated Press first disclosed details of the report Friday after obtaining a draft.

The study represents something of a capstone to a long debate over strategy, equipment and tactics used by the Forest Service, which faced questions after a relatively small fire on the afternoon of Aug. 26, 2009, turned into an inferno.

The document noted the blaze started in conditions ripe for intense wildfire: low humidity, high temperature and it began in 50-year-old dense shrubs and vegetation about 6 to 8 feet high, composed of more than 50 percent dry, dead material. It said that within about an hour of being reported, the fire covered approximately 15 to 20 acres.

It said seven helicopters and two air tankers were mobilized to respond to the fire during the first afternoon, with several aircraft arriving over the fire before 4 p.m. on the first day of the fire, on Aug. 26, 2009.

But an air tanker was nearby that never made it. The report said that tanker carrying fire-suppressing gel could have been diverted to the Station Fire, but accounts differed as to why that didn't happen.

Citing interviews, the report said a supervisor at the Station Fire believed firefighter efforts "appeared to be working" and did not have a site selected for the plane to release the gel, and a second official supervising the flight was concerned about approaching darkness. But the pilot told investigators darkness was not an issue and "he believed there was ample time for the tanker to fly to the Station Fire, make its drop, and return to base before nightfall."

The pilot "did not believe that the Station Fire aviation supervisor offered to find a location ... to drop its load," and believed the plane would interfere with helicopters over the fire, the report said.

But the report also notes large air tankers, typically used to dump retardant or water along ridge lines, might have had problems in the steep canyons where the fire was burning. "The tankers would have had to fly high enough to be safe from the power lines and the drops from such heights would likely have been ineffective," the report states.

Government records released after the blaze showed the Forest Service summoned several powerful firefighting airplanes in the early stages of the wildfire, then canceled and reordered them, causing a two-hour delay in their arrival on the second day of the fire. Recordings of calls between fire managers and dispatchers released last year showed the difficulty of communication in the mountainous region, and the problem of deploying aircraft as multiple fires burned in the state.

But the report found that because of rest requirements for flight crews and other issues, "it appears unlikely that any federal air tankers could have arrived over the Station Fire sooner than they did."

A federal review in 2009 found the fire slipped out of control because it jumped into steep, inaccessible terrain, not because the Forest Service scaled back firefighters and aircraft attacking the flames.

"We are not constrained by cost. We want to get the fire out," Forest Service Fire and Aviation Management Director Tom Harbour said at a congressional hearing earlier this year, defending the agency's response in the early hours of the blaze.

Federal foresters have long discouraged night flying because of the risk of operating aircraft in darkness in rugged national forests, but the agency reached an agreement with local firefighters earlier this year that makes it easier to get water-dumping helicopters into the air at night over the fire-prone Angeles National Forest. The Forest Service continues to review its own policies for night flights.

Critics have suggested that deploying waves of water-dropping helicopters could have slowed, or extinguished, the fire on its first night, before it raged out of control.

The report found the Forest Service requested a night-flying helicopter from the county about 5:30 p.m. on Aug. 26, but it was diverted to handle a medical emergency.

"Forest Service and Los Angeles County Fire Department officials told us that the recall of this helicopter did not affect the response to the Station Fire," the report said. Night flights were also discussed later that evening but officials decided "the gain from flying at night was not sufficient to warrant the risk."

The agency has argued that there are scant cases in which aircraft alone extinguish fires, since embers, brush and grasses on the forest floor can continue to burn even after a water or retardant drop.

Forest Service spokesman Joe Walsh said agency officials were reviewing the report and had no immediate comment.