FARNBOROUGH, England (Reuters) - The U.S. government must complete work on several specific foreign arms sales requests to demonstrate its efforts to accelerate the pace and predictability of the export process, the Pentagon's chief weapons buyer said.

"We have taken a number of steps to improve the rate, speed, pace and predictability of our export control processes. They are still cumbersome," U.S. Defense Undersecretary Frank Kendall said.

Kendall said U.S. weapons remained in high demand, but many other countries were rapidly developing and expanding their weapons capabilities. U.S. policy-related delays in approving U.S. arms sales were a growing concern in some areas, such as drones, he said.

"At this point, I think the advantages the U.S. has are still pretty strong. I‘m not sure if they’ll remain that way," he told reporters at the Farnborough International Airshow.

"With some systems, unmanned aircraft for example, policy matters start to affect the process, including the length of that process," he said. "We've made some progress there, but we still need to move some specific deals through to show that that’s real."

Kendall declined to comment specifically on fighter jet sales to Kuwait, Qatar and Bahrain that have stalled in the approval process, triggering growing frustration among those countries, and said those deals remained "under consideration."

U.S. military and industry officials have become increasingly vocal about the need to improve the arms sales process given years-long delays in the multibillion-dollar fighter sales to the Middle East.

Heidi Grant, deputy undersecretary of the U.S. Air Force, weighed in on Sunday, citing growing frustration among the key U.S. allies in the Gulf about delays in the process.

(Reporting by Andrea Shalal; Editing by Mark Potter)