CAPE CANAVERAL: Mars Pathfinder's long journey to the red planet must begin, like any other, with a single step. For NASA scientists, that first step was delayed again early Tuesday morning as Pathfinder's scheduled launch was scrubbed again for the second time in as many days. The weather, Monday's culprit, was near-perfect; this time a computer on the ground was to blame, failing with just over a minute remaining in the countdown. A backup computer also would not work, leading officials to suspect a software problem. NASA scientists say they must launch the $196M Pathfinder in December in order to intercept Mars' orbit or wait two years for another chance. "We're a museum piece if we don't launch by the 31st," said Curtis Cleven, launch operations manager. If successful, the craft will be the first-ever inter-planetary rover, slated to land on July 4, 1997. Several hours after Pathfinder parachutes down, the petals on the spacecraft will unfold; a six-wheeled, 23-pound rover will come out to roam the Martian surface, examining rocks and beaming back data. The launch has been tentatively rescheduled for Wednesday at 1:58 EST.