UPDATE 1-Pentagon F-35 chief sees no change in total buy

* Air Force still plans to buy 1,763 fighters; Navy 680

* Venlet says postponing production will add some cost

* Confident restructuring plan is realistic, achievable (Adds details from speech, quote, byline)

By Andrea Shalal-Esa

WASHINGTON, Feb 15 (Reuters) - The Pentagon on Tuesday said it remains committed to buying a total of 2,443 Lockheed Martin Corp (LMT.N) F-35 fighter jets despite a major restructuring that postponed production of 124 airplanes until after 2016.

"We have not changed our inventory objective," U.S. Navy Vice Admiral David Venlet told industry executives at his first public appearance since taking over as program manager of the Pentagon's largest acquisition program last May.

Venlet said the Air Force still planned to buy 1,763 of the stealthy new fighter jets, and the Navy planned to buy 680 for the Navy and Marine Corps, although it was considering whether to change its mix of carrier and short takeoff variants.

Decisions on that issue would be announced by the service chiefs in coming weeks, Venlet told a luncheon hosted by the National Aeronautic Association.

Venlet said he was confident that the latest restructuring, the program's second in less than year, was realistic and achievable because it was based on "very deep assessments" of all facets of the program, including technical issues, the manufacturing process, testing, and the supply chain.

Earlier reviews were more top down, while these assessments were bottom up, he noted.

Venlet said the decision to add $4.6 billion to the program was carefully and repeatedly vetted, and he was confident that the extra money would suffice to complete its development.

He said Pentagon acquisition chief Ashton Carter had told him that officials had been disappointed when earlier minor tweaks did not produce results. Venlet said he took it to heart when Carter told him, "I don't want to be disappointed."

The admiral acknowledged that postponing production of 124 jets as part of this restructuring on top of 100 jets already deferred earlier would drive up short-term unit costs since the program was still on a very "steep learning curve."

For the next few years, he said it would add in the range of $4 million to the cost of each airplane, tapering off to around $1 million in a few years.

Venlet said he had briefed the eight original partners and Israel on the details of the restructuring plan and its impact on cost, but he sensed continued commitment from the partners.

There had been no change in the plan to sell over 3,100 fighters to partner nations, although he said other countries would revisit their purchase commitments this year.

He said Japan, which had also expressed interest in the F-35 fighter program and had been briefed on its capabilities, could issue a request for proposals for new fighter jets soon.

"They're real serious and I think we'll have some important engagement with them this year," Venlet said.

Venlet said he supported Defense Secretary Robert Gates' drive to cancel development of an interchangeable engine for the F-35 that is being developed by General Electric (GEA.N) and Britain's Rolls Royce (RR.L).

Gates this week called the program "an unnecessary and extravagant expenses," and said he would look at all available legal options to close it down when a current stop-gap measure funding the government ends on March 4.

House lawmakers are due to vote later today or tomorrow on an amendment that would strip funding for the program out of a fiscal 2011 funding measure.

He said the debate over the second engine was driven by budget considerations, not questions about the engine makers' performance.

"This question about the engine is not about one company over another, one engine over another ... It's about constrained resources," he said, noting that he had flown military aircraft with all three engines, and all three companies offered great production and support.

Venlet acknowledged that the cost of the primary engine being built by Pratt & Whitney, a unit of United Technologies Corp (UTX.N) had risen by nearly $1 billion to account for too-optimistic previous cost estimates and to guard against some added risks. The final cost was still being negotiated. (Reporting by Andrea Shalal-Esa; Editing by Bernard Orr)