WASHINGTON - On a vacant piece of land near Nellis Air Force Base in Nevada, the promise of solar energy has collided into the demands of military training. And a solar project that would have featured a vast field of mirrors, a molten-salt storage facility and a 600-foot "power tower" appears to be heading for defeat.

In 2007, a Los Angeles firm called SolarReserve proposed the construction of a $700 million solar thermal power plant, covering two square miles near the Nevada Air Force base, where the sun shines brightly virtually all year long. There aren't issues with wildlife, the company said. Moreover, it could hook up its solar-powered turbines to existing transmission lines left behind by a defunct mining operation.

But Col. Howard Belote, installation commander at Nellis, said last week that the plan won't fly and is urging the government to turn it down.

The Air Force's opposition demonstrates some of the conflicts and delays that could lie ahead as renewable-energy projects search for places to put big wind turbines or solar collectors, even in Western states where the federal government is a major landholder. SolarReserve has been negotiating with the Air Force for 18 months and has already revised its plans once to move the plant 25 miles away from the base, at the Air Force's suggestion.

The Nevada plant was supposed to be a showcase for SolarReserve: one of the largest solar plants in the world, using heat-transfer technology developed for space rockets by United Technologies. A field of mirrors would focus sunlight on a receiver on a tall tower, where it would heat the molten salt to 1,050 degrees Fahrenheit, much hotter than other solar plants using similar technology. The molten salt would then flow to a storage tank, where its heat would generate steam and power conventional steam turbines similar to those in coal plants.

By using the molten-salt method, the plant could store 16 hours of power supply, easing concerns about the ability of solar plants to provide power when it is dark or cloudy. It would have a capacity of 100 megawatts, enough to power about 50,000 homes.

"We're trying to build a facility that runs 24 hours a day," said Kevin Smith, SolarReserve's chief executive.

But Belote said the solar plant would compromise classified aspects of the Air Force's training range and would interfere with radar. He said the Air Force would tell the Interior Department's Bureau of Land Management, which owns most of the land in the state, to reject the proposal. (The bureau controls more than 20 million acres of land with wind energy potential and more than 30 million acres with solar potential.)

SolarReserve officials "did a lot of (research) with publicly available tools," Belote said. "But when they came back for an official look the answer was, `Man, that's still too close.' And because of the sensitivity (of information), I can't tell them why. ... Unfortunately for them and us, there's stuff on the Nevada testing range we don't tell anyone about." Belote suggested they try another site, either 100 miles to the southeast or about 80 miles to the northeast, near the town of Mesquite.

Top executives at SolarReserve said they were upset and disappointed. They feel that the Air Force pointed them toward the second site before rejecting it. Moreover, the Nellis base boasts of its own photovoltaic panels - the nation' largest solar photovoltaic power plant; on May 27, Belote hosted President Obama and Senate Majority Leader Harry Reid, D-Nev., who toured the solar facility.

Obama "got a nice tour of the facility, but I expect he had not been informed that Nellis was resisting renewable-energy facilities in the surrounding area," Smith said. "The fact that Nellis AFB allowed someone to build a PV (photovoltaic) facility on the base and sell them the power is great, but they are hiding behind it while they try and stop other development in the region."

The Air Force has a history of balking at buildings near the 2.9-million-acre flight-training range in Nevada, which makes up 41 percent of the Air Force's total training acres worldwide. In the past, the service has objected to tall hotel projects in nearby Las Vegas and to wind turbines.

But Smith said "we tried to make sure we had a site the Air Force wouldn't object to." The company's plan would place a lone solar-power tower below a 2,000-foot-tall mountain range that separates their location from the base. The base sits well above the height of the tower.

In addition, the project would create many construction jobs, Smith noted.

SolarReserve is still hoping it can prevail upon the Air Force to approve the site near Nellis and has appealed to members of Congress for help. Belote has arranged for classified briefings to explain his objections to select Senate staffers, and he has promoted the project to the mayor of Mesquite, a small town just on the Nevada side of the Arizona border, 87 miles northeast of Las Vegas.

"Our community is very, very interested in alternative energy and the thought of being green," said Mesquite Mayor Susan Holecheck. "Historically, our economic base has been gaming and tourism."

Another solar company has already proposed a project using similar technology. Holecheck said the town would have to study whether a SolarReserve site would interfere with plans for moving the town's airport. And the Bureau of Land Management would also need to agree to provide land.

Smith hasn't had time to pursue the Mesquite idea. He said the Air Force just mentioned the alternative a month ago. "The difficulty with moving to a new site is you start over again," he said. "It is certainly something we can do if we fail at the current site but it will delay the project 12 to 18 months."