WASHINGTON, March 12 (Reuters) - The U.S. Navy's top officer on Tuesday said it would harm the overall F-35 Joint Strike Fighter program if the Navy completely scrapped its plans to buy 260 C-model planes that can land on carriers, but did not rule out a possible reduction in orders. Chief of Naval Operations Admiral Jonathan Greenert told an investor conference that the Navy was committed to the F-35 Joint Strike Fighter program and needed the new capabilities it offered, but the Lockheed Martin Corp was still working through technical challenges at this point. "We're in ... We need the F-35C; we need its capability. It has stealth, range, big payload capacity and an enormous electronic attack (capability)," Greenert told a conference hosted by Credit Suisse and defense consultant Jim McAleese. Greenert said the new plane's capabilities were "tremendous," but there was still expensive work to do on integrating the F-35 into the Navy's carrier air wings. "So the question becomes how many do we buy, and how does it integrate into the air wing," he said. "We are just sort of getting into the details of that." Greenert said any move by the Navy to eliminate its total purchase would increase the cost per plane of the other models, but would also have consequences for other countries interested in buying the C-model. "If we bought no Cs that would be very detrimental to the overall program because that's numbers," Greenert said, noting that any reduction in orders would raise the cost of the remaining planes to be purchase. Lockheed is building three models of the F-35 for three U.S. military branches and eight partner countries that helped fund the plane's development: Britain, Australia, Italy, Turkey, Norway, Denmark, the Netherlands and Canada. But rising costs, schedule delays and mounting budget pressures have forced some of the potential buyers to rethink their plans.