BEIJING, Sept.4 (Xinhuanet) -- U.S. forecasterson Sundaypredicted favorable weather as NASA began the countdown for the launching of the shuttle Atlantis, which is scheduled to lift-offWednesday.

The weather outlook indicated an 80 percent chance of favorable conditions with a small chance that low clouds or rain showers could force a delay, according to Kathy Winters, shuttle launch weather officer. Meanwhile, the three-day countdown for the shuttle Atlantis has begun at the Kennedy Space Centre.

NASA spokesman Bruce Buckingham saidthe crew is working around the clock to get the vehicle ready, "There is no wiggle room here at all."

This is the second time a countdown was started for this mission of Atlantis, which originally was to blast off Aug. 27. The launch was delayed after lightning struck the launch pad, requiring engineers to check for damage to Atlantis' systems.

Atlantis will kick off a final spate of space station assembly missions that must be finished by 2010, when the shuttle fleet is to be retired.

The shuttles are the only vehicles designed to carry the station's major components to orbit.

The 100 billionU.S.dollars international orbital outpost was about half finished when NASA lost the space shuttle Columbia and its seven astronauts on Feb. 1, 2003.

The weather outlook at the Florida shuttleport remains favorable through backup launch opportunities for Atlantis on Thursday and Friday. But, if Atlantis willnot be launched by Friday, NASA has agreed to postpone the mission again so the Russians can launch a new two-man resident crew to the space station on Sept. 18. Enditem