The Air Force is holding up construction of an Oregon wind farm that would be the largest in the country amid concerns that the farm's 300-plus new turbines will interfere with transmissions from a radar station in Fossil.

, developer of the

wind energy project in north-central Oregon, has its construction contractor on site and hopes to break ground May 1. The project will provide 706 construction jobs and millions in royalty payments for farmers and ranchers in Gilliam and Morrow counties, Caithness says.

But the

, with backing from the

, issued a "notice of presumed hazard" in March, barring construction of any towers above "0 feet." The company hasn't been able to resolve the issue, even with Oregon Sens.

and

trying to run interference.

"We're just sitting here in no man's land," said Les Gelber, a Caithness Energy partner.

Air Force officials could not be reached for comment late Wednesday, and it's unclear how many other potential wind farms are affected. Last month, the industry said more than a dozen projects are stalled.

The FAA is still evaluating Shepherds Flat, spokeswoman Sasha Johnson said by e-mail. "This project is still in process and we are working with all parties to gather information."

Wyden said he worries that the Air Force concerns could thwart big wind farms in the pipeline throughout rural Oregon and nationwide. His technical advisers tell him the radar problems are solvable without compromising military security, he said.

"If the Defense Department allows this project to go down the drain after years and years of development, the (wind farm) investors are going to walk," Wyden said. "We don't see why they should be able to come in at the last minute and put the kibosh on this program."

also hopes to begin construction in May on three wind projects with a total capacity of 400 megawatts, one in Gilliam County and two in Washington's Klickitat County.

Spokeswoman Jan Johnson said the company received clearance from the FAA in 2008 and 2009 on those projects, but had to reapply after making minor modifications. The company has not heard back from the FAA on the new applications, she said.

Air Force Gen. Gene Renuart, head of

, testified before Congress in March that the military is increasingly concerned about wind farms disrupting radar. The number of U.S. wind projects is growing fast amid increasing demand for renewable energy and plentiful government subsidies.

Caithness wants to erect 338 turbines with a total capacity of 845 megawatts. That's well above the capacity of

coal-fired plant near Boardman, though wind power is relatively sporadic.

Gelber said Caithness has been through four to five years of permitting with county, state and federal governments, ironed out concerns with the Navy, and notified the Air Force about the project three years ago. At that point, Gelber said, "The Air Force looked at this and went away."

The company has inked a $1.4 billion deal with

to provide the turbines. Workers have begun arriving on site to build roads and turbine foundations, Gelber said, but the contractor is now telling them to stand down.

The FAA's notice said all the proposed turbines would be located within radar line-of-sight of the Fossil radar station, which Caithness said was built in the 1950s about 50 miles from the Shepherds Flat site.

The Shepherds Flat turbines -- combined with about 1,800 other turbines built or proposed within the Fossil station's range -- would "seriously impair the ability of the (Department of Defense) to detect, monitor and safely conduct air operations in this region," the notice said.

There is no overlapping radar coverage in the area, the notice said, and the station "already experiences significant clutter and target tracking issues in this general area."

The tall turbines can reflect radar signals, creating a blind spot that can erase airplanes on radar screens. The turbine's rotating blades can also clutter the screens, creating a radar signature that constantly changes as the blades slow down or speed up in the wind.

Industry officials say they're working on radar friendly turbine technologies. Upgrades to radar stations -- possibly financed by the wind farms -- would also help. Modern systems are much less affected by spinning turbines.

Gelber said he hopes to iron out the issue with the FAA and the Air Force. But he hasn't been able to get detailed analysis of the radar problems posed by Shepherds Flat from the military.

The company has all its required permits, Gelber said. "We're not asking for special treatment here."

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