WASHINGTON (Reuters) - The Pentagon said on Wednesday its fiscal 2016 budget proposal will fund early technology development and prototyping of a "next-generation X-plane" that would eventually succeed the F-35 fighter jet being developed and built by Lockheed Martin Corp.

Defense Undersecretary Frank Kendall, the Pentagon's chief arms buyer, said the funding would be part of a new "aerospace innovation initiative" aimed at ensuring that the U.S. military continued to dominate the skies despite development of so-called fifth-generation stealth fighters by China and others.

He told the House Armed Services Committee the initiative would be headed by the Defense Advanced Research Projects Agency, with help from the Air Force and the Navy.

Speaking with reporters during a break in the hearing, Kendall declined to give details on the amount of funding involved in the new initiative since the Pentagon's budget will not be delivered to Congress until Monday.

Lockheed, Boeing Co and Northrop Grumman Corp have urged the department to start funding a new major aircraft development program given the dearth of new programs in recent years.

Kendall said the new project was meant to ensure continued work for industry design teams as development of the F-35 neared an end.

He told reporters the project would also include work on development of a next-generation propulsion system, which has already been funded under a separate program.

Kendall said it was not yet clear if the new aircraft would be manned or unmanned. He said there have been promising developments in hypersonic technology, but it would not be practical to build an aircraft as large as a fighter using that technology.

(Reporting by Andrea Shalal; editing by Matthew Lewis)