By Irene Klotz

CAPE CANAVERAL, Fla., June 14 (Reuters) - U.S. and Russian flight controllers partially restored critical computers aboard the International Space Station on Thursday after a system crash that could have forced the $100 billion orbital outpost's crew back to Earth.

The U.S. space agency NASA also made plans to keep the visiting space shuttle Atlantis attached to the station for an additional day to help steer the massive complex if the computers, which control navigation, remain a problem.

Flight directors told the crew to cut power to non-critical equipment, such as lighting, to conserve electricity and fuel in case the shuttle's mission to the space station is extended.

"We're just trying to buy some margin for an extra docked day," astronaut Shane Kimbrough from Mission Control in Houston radioed to the crew.

In a worst-case scenario, the computer woes could have forced the three astronauts aboard the space station, including NASA's newly arrived Clayton Anderson, to leave the outpost in the station's escape ship, a Russian Soyuz capsule.

As a precaution, the Soyuz was put on battery power on Wednesday for seven hours before the two Russian computers were successfully rebooted early on Thursday, allowing the capsule to be returned to station power.

Engineers were not sure what was causing the problem with the Russian computers, but the glitches began shortly after a newly installed solar wing panel began producing power.

NASA plans to fold up the second half of an older solar wing panel that must be moved before the new array can rotate and track the sun for full power.

Spacewalking astronauts Patrick Forrester and Steven Swanson helped guide the old wing into its storage box during an outing on Wednesday. Their crewmates James Reilly and John "Danny" Olivas will finish the job during a spacewalk on Friday.

Reilly and Olivas also are scheduled to repair a bit of protruding insulation near the rear of the shuttle. A corner of the blanket tore lose during Atlantis' launch six days ago, potentially exposing inner layers of the shuttle's surface to superheated gases on re-entry.

NASA has already extended Atlantis' mission from 11 to 13 days and added a fourth spacewalk to make sure there was enough time to fix the heat shield and retract the old solar wing.

The astronauts must also prepare other station systems for the arrival of new laboratory units and life support equipment for an expanded, six-person resident crew.

The U.S. space agency has three years to finish building the complex before the shuttles, which are the only vehicles capable of hauling major components and assembling the station in orbit, are retired.

The station, a project of 16 nations, is a little more than half finished.

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