(Corrects 12th paragraph to show 10 countries besides U.S. haveordered jets, removes reference to Canada)
By Andrea Shalal and Idrees Ali
WASHINGTON, Aug 2 (Reuters) - The U.S. Air Force will onTuesday declare an initial squadron of Lockheed Martin Corp F-35A fighter jets ready for combat, according tosources familiar with the decision.
U.S. General Hawk Carlisle, who heads Air Combat Command,will announce at a news conference at 1:00 p.m. EST (1700 GMT)that the Air Force has an "initial operational capability" ofthe F-35 jets, said the sources, who were not authorized tospeak publicly.
The decision marks another big milestone for the $379billion program, the Pentagon's largest weapons project. The AirForce follows the U.S. Marine Corps, which declared a firstsquadron of F-35s ready for combat in July 2015.
Officials say the F-35 will give the U.S. military theability to detect enemy aircraft and other threats far beyondcurrent ranges, allowing the jets to strike targets anddisappear long before they are detected.
The U.S. Air Force plans to buy a total of 1,763 F-35Aconventional takeoff and landing jets in coming years and willoperate the largest F-35 fleet in the world.
Carlisle told reporters last month he was "very confident"in the new stealthy warplane, and lauded its performance duringa practice deployment to a second air base, where the jetssuccessfully completed all 88 missions planned.
At the time, Carlisle said the declaration would mean theAir Force could use the jets for combat deployments to theMiddle East or elsewhere if needed.
The Pentagon's F-35 program office on Monday announced thatthe F-35A had launched an AIM-9X air-to-air missile to hit and"kill" a target simulating a drone over a military test rangeoff the California coast on July 28.
"After launch, the missile successfully acquired the targetand followed an intercept flight profile before destroying thedrone, achieving the first F-35 air-to-air kill or 'BoolaBoola,' which is the traditional radio call made when a pilotshoots down a drone," the program office said.
The same F-35 pilot who hit the drone also used aninternally carried AIM-120C missile against another target dronethat was beyond visual range, telling it to self-destruct rightbefore impact, the program office said in a statement.
"It's been said you don't really have a fighter until youcan actually hit a target and we crossed that threshold with thefirst air-to-air weapon delivery of an AIM-9X," said Air Forcetest pilot Major Raven LeClair.
Lockheed is building three models of the F-35 Lightning IIfor the U.S. military and 10 countries that have already orderedthe jets: Britain, Australia, Norway, Italy, Turkey, Denmark,the Netherlands, Israel, South Korea and Japan.
The Pentagon's F-35 program office said it remained innegotiations with Lockheed about long-delayed contracts for thenext two batches of F-35 jets, deals worth about $15 billion.
"We're seeking a fair deal for the F-35 enterprise andindustry," said F-35 program spokesman Joe DellaVedova.
The program, first launched in 2001, has made strides inrecent years after huge cost overruns and technical problemsthat sent the project cost up by nearly 70 percent.
Earlier problems with the fighter jet included issues withthe radar software and complications which increased the risk ofneck injury to lightweight pilots during the catapult of theseat. The issues have since been fixed.
Industry and U.S. defense officials say they are workinghard to continue driving down the cost of the new warplanes toaround $85 million per plane by 2019, as well as the cost ofoperating the jets.
"The program is not doing everything they wanted it to do...But they're at a point now where it is stabilizing and so it isprogress," said Todd Harrison, a defense analyst at the Centerfor Strategic and International Studies. (Reporting by Andrea Shalal and Idrees Ali. Additionalreporting by David Alexander.; Editing by Madeline Chambers andMarguerita Choy)