WINDSOR LOCKS, Conn. — Pratt & Whitney, a United Technologies

[UTX] company, expects its military jet engine business to grow over the long run as construction of the F-35 Joint Strike Fighter ramps up, but it will first have to weather a lull in the next couple years with production winding down on engines for earlier aircraft, its top executive said yesterday.

Pratt & Whitney President Dave Hess told reporters at its annual media day that it will deliver 50 F-135 engines for the JSF this year and will stay at about that number annually for the next several years until production of the of the Lockheed Martin [LMT]-built F-35 Lightening II picks up. With the yearly rate currently leveled out until the middle of this decade, the number of military engines produced by the company in the next couple years will fall as it concludes production of F-100 spare engines for the F-22 Raptor, he said.

“There certainly is a little bit of a near-term challenge,” Hess said.

“We are in a little bit of a transition period on the military programs, going from legacy engines to new engines,” he later added.”We just have to navigate through a couple of transitional years in our business.”

Hess acknowledged that some production could “drop a little bit” from the current plan due to budgetary pressures at the Pentagon, which in February announced a proposal to defer construction of 179 JSFs outside of the five-year plan that begins in fiscal 2013. The Pentagon said the move will save $15 billion and allow more time to mature the airplane that has experienced technical problems and massive cost overruns.

But Hess said Pratt & Whitney is well positioned after becoming the sole source for the Joint Strike Fighter engine following a decision by Congress last year to eliminate the alternative engine offered by a General Electric [GE] and Rolls-Royce partnership. He said he does not expect defense cuts or possible sequestration to have a major impact on its jet engine business.

“The military engine business looks great for us because we’re on the right program,” he said. “We’ve got sole source position on the Joint Strike Fighter, which, I think, regardless of where the debate ends on sequestration and some of the defense budget cuts, that is going to be a growth engine.”

Pratt & Whitney will also get a boost when it moves into production later this decade of the PW4062 engine for the Air Force’s next generation aerial tanker, Boeing‘s [BA] KC-46A, Hess said.

By the 2020, Pratt & Whitney projects sales to double across its commercial and military engine businesses from $12 billion in 2010 to $24 billion, he said.