The Marine version of the F-35 Joint Strike Fighter, already more than a decade in the making, was facing a crucial question: Could the jet, which can soar well past the speed of sound, land at sea like a helicopter?/…/With a record price tag — potentially in the hundreds of billions of dollars — the jet is likely to become a target for budget cutters. Reining in military spending is on the table as President Obama and Republican leaders in Congress look for ways to avert a fiscal crisis. But no matter what kind of deal is reached in the next few weeks, military analysts expect the Pentagon budget to decline in the next decade as the war in Afghanistan ends and the military is required to do its part to reduce the federal debt.