Evergreen International Aviation, which operates a hangar at Pinal Air Park north of Tucson, has spent more than $10 million creating a "supertanker" capable of dropping 24,000 gallons of water on wildfires, seven times the load carried by a standard air tanker. The plane is expected to be ready by Sept. 1, and Evergreen administrators hope the U.S. Forest Service will begin leasing the aircraft as early as next summer.

"This could mean the difference between a small fire and a tragic, massive wildfire," said Cliff Hale, Evergreen's vice president for special projects.

But some government officials and critics of the plan are skeptical of Evergreen's concept, saying the company is touting an ineffective aircraft that won't hit its targets and can't fly low enough to make a difference in a forest fire.

"Bigger may not necessarily be better," said Rose Davis, a Forest Service spokeswoman at the National Interagency Fire Center in Idaho. "We're certainly not jumping up and down about this."

The supertanker, which can fly as low as 400 feet above the ground, is equipped with a row of large tanks filled with water or fire retardant. Additional tanks loaded with compressed air will force the liquid out of four holes the size of frying pans in the jetliner's belly.

Although standard heavy air tankers used for years to battle wildfires cost an average of $5,000 an hour to operate, the rate for the supertanker could exceed $20,000 an hour, a bill that would be footed by taxpayers.

Government officials are concerned that the tanker has yet to receive its mandatory Federal Aviation Administration safety certification, and it remains unclear whether such a large load of water could injure firefighters working on the ground, Davis said.

In addition, she said the 747 cannot fly nearly as low as standard air tankers, which descend to about 150 feet, and its massive size limits the number of air bases where it can take off and land.

The supertanker project also has raised the ire of some air tanker pilots whose contracts were eliminated by the Forest Service earlier this year amid safety concerns regarding the planes.

Pilots who flew the decades-old tankers say they would rather the government focus on revamping the fleet and bolstering their airborne firefighting programs. To some, the public's interest in the supertanker is a slap in the face.

"We've been out there for a long time, and we've proven to be capable of doing the job," said Leonard Parker, president of the Nevada-based Minden Air Corp., which saw its tanker contracts terminated earlier this year. "I think we need to spend more money on the firefighting program. We have a well-established system that we need to spend money on right now."

Evergreen officials rebut allegations that the supertanker will become the latest taxpayer-funded boondoggle, but they acknowledge that the jetliner would not be effective in some scenarios.

"We're not saying this is going to be the best tool there is. It is simply another tool," Hale said. "If you take the right combination of tools, you'll get the best result."

The first supertanker is undergoing final safety checks, while maintenance workers are aboard the gutted plane 24 hours a day making adjustments to the aircraft, he said.