UPDATE 1-Pentagon said planning to extend Lockheed F-22 line

(recasts, adds details, background)

WASHINGTON, Nov 30 (Reuters) - Defense Department officials are planning to extend production of Lockheed Martin Corp's LMT.N F-22 fighter jet amid concerns over the airworthiness of the aging fleet it is replacing, a senior Pentagon official and a person noted for close ties to the Pentagon said on Friday.

“Pentagon insiders say the Office of the Secretary of Defense is planning ... to continue production” beyond the 183 F-22s due to be delivered by the end of 2011, said Loren Thompson of the Arlington, Virginia-based Lexington Institute, noted for links to the Pentagon and industry.

“Policymakers are under pressure ... because Cold War fighters are falling out of the sky due to age,” he added, referring to the Nov. 2 crash of an aging F-15C that prompted grounding of much of the F-15 fleet twice this month.

Representatives of the Air Force and the Defense Department did not immediately return calls seeking comment.

A spokesman for Lockheed Martin, Rob Fuller, said: “We stand by to support our customer as needed.”

The U.S. Air Force grounded all of its Boeing Co. BA.N F-15A, B, C and D models this week -- 442 planes -- amid fears of catastrophic failure near where the canopy meets the airframe. The most modern model, the F-15E, continues to fly.

A senior Defense Department official said planning was under way to keep the F-22 line open beyond its currently scheduled end after 183 aircraft are delivered.

“The grounding of F-15s is focusing attention on the issue at high levels,” said the official, who asked not to be named because discussions about the matter are continuing.

The second F-15 grounding, ordered on Wednesday, reversed a decision to resume operations after inspections prompted by the Nov. 2 crash of a nearly 30-year-old Missouri Air National Guard F-15C while on a training flight.

The F-22s, the top U.S. air-to-air fighter, have a flyaway price of about $132 million each. Congress has approved $3.15 billion to procure 20 F-22s in fiscal 2008, which began October.

In addition, Lockheed Martin is under contract from the Air Force to supply 40 more F-22s, at a rate of 20 per year, through the end of 2011, when production is scheduled to end.

The F-22 is produced in partnership with Boeing and Pratt & Whitney, a United Technologies Corp UTX.N unit that supplies the engines.

Thompson, citing insiders, said money was being put into the fiscal 2009 budget to buy “long-lead” items needed to go on manufacturing the F-22 after the last batch of 20 are delivered.

The Air Force has been pressing in recent years to buy 381 of the radar-evading F-22s, up from the 183 limit previously imposed by the Pentagon. (Reporting by Jim Wolf; Editing by Carol Bishopric)