* Britain to get first F-35 to go to a U.S. partner * Pentagon has delayed production, revamped program 3 times * Lockheed Martin program said to have made "considerable strides" By Jim Wolf July 18 (Reuters) - Britain and the United States hailed Wednesday their work on Lockheed Martin Corp 's F-35 Joint Strike Fighter as tightening military ties, a day before Britain receives the jet's first international delivery. Britain is to formally accept an F-35 test model at Lockheed's Fort Worth, Texas, production plant on Thursday. The Pentagon seized the occasion to voice strong support for the plane, which is over budget, behind schedule and a potential target for cuts by lawmakers. The delivery reflects "considerable strides" in the program, particularly in the past year, U.S. Defense Secretary Leon Panetta told a Pentagon press conference alongside Philip Hammond, his British counterpart. "The F-35 represents, I believe, the future of tactical aviation for both of our armed services" and would help ensure "our dominance of the skies for years to come," he said. Hammond, Britain's secretary of state for defense, cited joint work on the F-35B short takeoff/vertical landing model -- of which Britain plans to buy 48 -- as one of the "crucial keystones" of what he called Britain's most important defense relationship. The radar-evading, multirole F-35 is the Pentagon's costliest arms purchase, expected to top $396 billion for 2,443 aircraft in three models through the mid-2030s. The aircraft is being built for the U.S. Air Force, Navy and Marine Corps along with Britain and the seven other co-development partners - Italy, Turkey, Canada, Australia, Denmark, Norway and the Netherlands. Israel and Japan also are buying the F-35, designed to replace a range of fighter, strike and ground-attack aircraft, including Lockheed's multirole F-16, the world's most widely used fighter. The Defense Department this year postponed production of 179 F-35s until after 2017, stretching development and testing in an effort to curb costly retrofits. The project's latest restructuring, the third such major revamp, added 33 months and $7.9 billion to the development plan. "Our continued commitment to this program will also further solidify the U.S.-U.K. alliance," Panetta said. He handed over a small-scale model, joshing that it was a cheaper version of the one for which Hammond is to pick up the keys in Texas. Lockheed Martin, the Pentagon's No. 1 supplier by sales, is developing the F-35 with Northrop Grumman Corp and Britain's BAE Systems PLC. Britain initially invested $2 billion in the F-35's development, the most of any of the eight partner nations. Hammond later in the day cheered the F-35B model as "superb" and as an example of the "merit of cooperating more fully - pooling demand, investment and technology." "And no two countries are better placed to work together for the common good than Britain and the U.S.," he said in a speech hosted by the Center for a New American Security, a private national security research group. Hammond told Reuters before his speech that Britain ultimately planned to buy an unspecified number of additional F-35 models after deciding - as early as 2015 or as late as 2020 - on a mix of manned and unmanned aircraft to replace its multirole Eurofighter Typhoon fighters.