"We've been having that conversation for over a decade," Chief Executive Robert Stevens said in an interview. Pressed on his current expectation when it would close, he shot back: "We'll have that conversation for over a decade."

As recently as last year, the last jet had been projected to emerge from the company's Fort Worth, Texas, plant by mid-2013 unless new export orders came.

They did. Lockheed is now building F-16s for Egypt, Oman and Iraq - enough to keep the line going until at least January 2016, Joseph LaMarca, a company spokesman, said by email.

More than 4,500 F-16s have been delivered to 26 nations since production began in 1975. Major upgrades to all F-16 versions are being offered by Lockheed, the Pentagon's No. 1 supplier by sales.

Stevens said he expected continuing demand for the F-16 even as customers start to trade up to Lockheed's radar-evading F-35 Joint Strike Fighter, now in early production.

"We'll certainly have a line in position to satisfy that demand," he said in an interview with Marillyn Hewson, the chief operating officer who is to replace him as Lockheed CEO effective January 1.

One significant potential customer is Taiwan, which has sought as many as 66 new F-16C/D models for years. Lockheed representatives steered questions about any such sale to the governments involved.

President Barack Obama's administration told Senator John Cornyn in a letter dated April 27 that it shared his concerns about Taiwan's "growing shortfall" in fighter planes as its F-5s are retired, notwithstanding an upgrade of 145 early-model F-16A/Bs that is getting under way. Cornyn is a Texas Republican.

The White House promised him at the time that Mark Lippert, a new assistant secretary of defense for Asian & Pacific security affairs - whose nomination to the job previously had been blocked by Cornyn to press for the sale - would seek a "near-term course of action" to address Taiwan's fighter gap, "including through the sale to Taiwan of an undetermined number of new U.S.-made fighter aircraft."

Sampson Li, director of the military mission of the Taipei Economic and Cultural Representative Office in Washington, declined in an emailed statement to comment directly on whether Taiwan still wanted new F-16s now that the A/B upgrade is to begin.

"Our future procurement of advanced fighters from the United States should be comprehensively evaluated by both sides to conform to Taiwan's future defense needs," he said.

Rupert Hammond-Chambers, president of the U.S.-Taiwan Business Council, said Taiwan's fighter gap was becoming more "acute" as the upgrade of its A/B models took them out of service temporarily.

"It is clear that the White House sees the sale of new fighters as part of its future commitment to Taiwan," he said by email.

A spokesman for Cornyn, Drew Brandewie, said that the United States was obligated to make sure Taiwan can defend itself against China, which deems the self-governing island a rogue province subject to a return to the fold, by force if necessary.

Asked whether Cornyn might use his senatorial privilege again to hold up confirmation of President Barack Obama's nominees, Brandewie said in an email that all options were being left open.

In December, the administration notified the U.S. Congress of plans to sell a second batch of 18 F-16s to Iraq, a deal that is expected to close soon.

In addition, Romania and Bulgaria are among those interested in either second-hand aircraft or new models, said LaMarca, the Lockheed spokesman.

(Reporting By Jim Wolf; Editing by Tim Dobbyn)

By Jim Wolf