By Andrea Shalal

FARNBOROUGH, England (Reuters) - A top U.S. Air Force official on Sunday urged the U.S. government to speed up consideration of long-standing bids by Qatar, Kuwait and Bahrain to buy U.S. fighter jets, citing growing frustration among the key U.S. allies in the Gulf about delays in the process.

Air Force Deputy Undersecretary Heidi Grant said she was trying to reassure those countries that Washington's failure to approve billions of dollars of U.S. arms sales to them would not alter their strong bilateral air force-to-air force relationships with the United States.

"I would like to see a decision soon," Grant told Reuters in an interview on the eve of the Farnborough Airshow in southern England. Grant said she "absolutely" saw growing frustration among officials in the three countries, which have asked to buy a variety of U.S. fighter planes.

"It's caused us to do more to reassure them that this one transaction should not impact the larger relationship ... that they are very valued partners," she said. "Hopefully the delay in this decision to move forward isn’t going to have any impact."

Grant said the three requests were still being worked on "at the highest levels of our government." She declined to comment on what was holding up the decisions.

All three arms sales have stalled amid concerns raised by Israel that equipment sent to Gulf states could fall into the wrong hands and be used against it, and by the Obama administration's desire to integrate arms sales decisions into its broader decision-making on military aid to the Gulf.

The Pentagon and State Department have both have signed off on the sale of 36 F-15 fighter jets to Qatar for about $4 billion, and 24 F/A-18E/F Super Hornets to Kuwait for about $3 billion, both built by Boeing Co, according to sources familiar with the matter. A third deal would sell about 16 Lockheed Martin Corp F-16 fighter jets to Bahrain in a deal valued at just under $1 billion.

The White House has not yet approved the sales, although the Kuwait sale at least is expected to see approval before the Obama administration leaves office, the sources said.

Leanne Caret, chief executive of Boeing Defense, Space & Security, told reporters the approval process was clearly taking longer than the company would like, but Boeing's Middle East customers were "hanging in there with us" despite the delays.

"I believe we have a bright future on it, and we look forward to resolving it soon," she said.

Grant joins other military officials and lawmakers who have urged the Obama administration to move forward on the arms sales requests, some of which have been in work for years.

David Melcher, president of the U.S.-based Aerospace Industries Association trade group, said the delays could be particularly hard on smaller firms in the weapons supply chain to manage, and gave U.S. competitors a big advantage.

"Whole markets have been created out of the lag, and that to me, is something that is not in the interest of the U.S. or U.S. industry," he told Reuters in an interview.

Melcher said Vice Admiral Joe Rixey, who heads the Pentagon's Defense Security Cooperation Agency, was working to help streamline the approval process for foreign arms sales. He said Rixey explored bottlenecks in the process with about two dozen industry executives during a tabletop exercise in May.

U.S. Navy Secretary Ray Mabus last month warned the U.S. Navy could see the cost of new F/A-18E/F Super Hornets rise unless the government approves foreign sales of the jets soon.

Mabus said he was frustrated by delays in approving the sale of the Boeing jets to a close U.S. ally.

Senior U.S. officials have said they are keen to see the Boeing F-15 and F/A-18 production lines in St. Louis, and the Lockheed F-16 line in Fort Worth, Texas, continue, and do not want to foreclose options on fourth-generation aircraft.

(Editing by Mark Potter)