WASHINGTON (Reuters) - Lockheed Martin Corp’s new F-35 fighter jet may be delayed by up to three years and its development cost could increase by up to $5 billion, sources familiar with the program said on Monday.

Navy Vice Admiral David Venlet briefed Pentagon acquisition chief Ashton Carter on Monday about the draft results of a comprehensive review of the program, said the sources, who were not authorized to speak on the record.

The review was conducted to prepare for a high-level meeting of the Pentagon’s Defense Acquisition Board that is scheduled for November 22, the sources said.

The Pentagon has estimated the cost of the F-35 program could reach $382 billion over time, its costliest weapons program ever. The program was restructured earlier this year, adding 13 months to the development phase.

The latest delays stem from problems with software development for the new radar-evading fighter, and technical problems with the short takeoff and landing Marine Corps version of the new fighter, the sources said.

They said the Air Force and Navy versions of the fighter would need an additional year of development, while the Marine Corps version would need two to three years longer.

The cost increase is linked mainly to demands by Pentagon officials for additional testing of the new fighter before the plane can be used on the battlefield, said analyst Loren Thompson of the Virginia-based Lexington Institute.

He said further delays and cost increases in the program would be a setback for Lockheed, given that the F-35 is the company’s biggest program.

Pentagon spokeswoman Cheryl Irwin said it was premature to discuss anything about the program.

Lockheed spokesman John Kent said it would be premature to discuss the results of the review until the findings of the November 22 Pentagon meeting are released.

Lockheed shares closed 18 cents higher at $71.47 despite news about the F-35 program.

CRITIC’S CONCERNS

Winslow Wheeler, a budget analyst with the nonpartisan Center for Defense Information, said the latest news underscored his longstanding concerns about the program.

“This airplane should never have happened. It’s too expensive, too complex, and too modest performance,” he said. “It’s a cost and performance disaster.”

The United States is co-developing the F-35 with eight foreign partners -- Britain, Italy, the Netherlands, Turkey, Canada, Australia, Denmark and Norway. The U.S. military services are due to buy 2,457 of the new fighters, with the international partners to buy an additional 730 planes.

But rising costs and development delays have begun to erode confidence in the program, especially given budget constraints in many partner countries.

Britain last month announced major cuts in defense spending, and a top military official on Monday confirmed his country would not buy all 138 F-35 fighters initially planned.

“It will be less than the original 138,” General Nicholas Houghton, vice chief of Britain’s defense staff, told reporters before a conference in Washington.

He said the final number will depend on many factors still being weighed, including work on a new unmanned combat aerial vehicle, and plans for land-basing new fast jets.

“I don’t want to over-specify a figure because the work has not yet been done,” Houghton said.

Canada’s opposition Liberal Party last week also said it would scrap a C$9 billion ($8.7 billion) deal to buy the F-35 if it won the next general election, widely expected to be held next year. The minority Conservative government announced the sole-source deal with Lockheed in July but has not yet signed a contract.

Britain’s decision to skip buying the Marine Corps version could signal the end of that variant, several analysts said, noting it was experiencing problems with the inlet doors for the lift fan needed to allow short takeoffs and landings.

Houghton said Britain decided to opt for the carrier version being developed for the U.S. Navy instead, because it offered more payload and greater range.

Wheeler said Britain’s decision probably also reflected concerns about the rising cost of the short takeoff version, its higher maintenance and procurement costs, and the fact that its testing schedule was furthest behind.