The U.S. military's technological superiority is increasingly challenged by China, and efforts to maintain an edge are complicated by shrinking defense budgets that have cut money for development, the Pentagon's top weapons buyer said on Tuesday.

Frank Kendall, the deputy undersecretary of defense for acquisition and technology, told lawmakers the U.S. military's technological superiority is being "challenged in ways that I have not seen for decades, particularly in the Asia-Pacific region," where China is pursuing a rapid modernization program.

"Technological superiority is not assured," Kendall told the Armed Services Committee in the House of Representatives. "This is not a future problem. This is a here-now problem."

With China, Russia and other countries rapidly modernizing their militaries, Pentagon officials are voicing increasing concern about the possibility of losing the technological edge that has enabled the U.S. military to dominate the battlefield over the past 25 years.

U.S. defense officials say they do not expect a conflict with China or Russia, but the chances are that some of what they develop will be sold to other nations and the U.S. military may eventually face those systems.

Defense Secretary Chuck Hagel underscored the value of advanced research in a visit this month to Sandia National Laboratories in New Mexico, saying the "technological edge that we've been able to maintain is critically important ... in the world that we're in today with more complications, more combustibility."

Admiral Samuel Locklear, the head of U.S. Pacific Command, told reporters in Washington recently the military's "relative dominance" had been diminishing after a period of unequalled superiority.

"That's not something to be afraid of; it's just to be pragmatic about," Locklear said, adding that the military would have to think carefully about which systems to develop in the future in order to maintain that edge.

Asked by a lawmaker how the technology race with China was going, Kendall indicated it was not positive, even though U.S. defense spending is far greater than China's.

The base U.S. defense budget will drop below $500 billion in 2014 under a deal finalized in January, while China's grew to $119 billion last year after another double-digit jump.

"Overall, China's military investments are increasing in double-digit numbers each year, about 10 percent," Kendall said. "Their budget is far smaller than ours. But their personnel costs are also far smaller than ours."

Personnel costs make up roughly half of the U.S. defense budget.

Kendall told lawmakers the Pentagon's ability to respond by developing new technologies was "severely limited by the current budget situation," with the department facing hundreds of billions in cuts to projected spending over the next decade.

Lawmakers voiced concern about not having known about Pentagon concerns earlier and asked Kendall when he first realized U.S. technological superiority was being challenged.

"We've had a steady decline (in spending) over the last several years of cuts ... We've been pleading with you guys to come over and tell us the problem," Representative Randy Forbes of Virginia, a Republican, told Kendall.

Kendall said the issue became "a more visible concern" when the department conducted a strategic review after Congress approved the budget cuts in 2011.