NASA mission managers, consequently, could end up with only two options: Keep the seven-member crew in orbit an extra day or re-route the shuttle to a back-up landing site at Edwards Air Force Base in California, where clear weather is expected all week.

"Just to let you know, the weather is not good at the Cape at the moment. We are expecting it to be poor all week," astronaut Scott Altman told the crew from NASA's Mission Control Center in Houston.

"However, there is still a chance. The weather forecasters think [Tuesday] might be one of best chances to get into the Cape," Altman added. "We're hoping that things break our way [Tuesday] morning and we'll be able to get you all down at the Cape."

A second and final opportunity to land at KSC Tuesday will come at 10:39 a.m. EDT (14:39 GMT). The astronauts will have two chances to land at Edwards. Those will come at 12:11 p.m. EDT and 1:47 p.m. EDT (16:11 GMT and 17:47 GMT).

The U.S. space agency prefers to land shuttles at its coastal Florida spaceport. It costs about $1 million, and can take a week or two, to ferry a shuttle from California to Florida atop a modified 747 jumbo jet.

With good weather expected at Edwards all week, NASA flight director Leroy Cain said mission managers likely would opt to keep the shuttle up an extra day if conditions prohibit a return to Florida on Tuesday.

The Endeavour astronauts, meanwhile, also prefer to land at KSC, where their families and friends have gathered for an end-of-mission homecoming.

"My preference is to come back in to Florida. I love that area. I've landed there on my other flights," Endeavour commander Kent Rominger, a veteran of four previous shuttle missions, told reporters during a space-to-ground news conference.

"But we want to do what's right, and if the weather is not good [at KSC], then we'll have to go into Edwards if the weather is good there."

Nonetheless, Rominger said he hopes the weather in Florida won't be as bad as predicted.

"Knock on wood," the shuttle skipper said. "Forecasters have been off before, so I'm somewhat optimistic that they may be off a little bit this time and we can sneak in there."

Launched from KSC April 19, the Endeavour astronauts delivered a new Canadian construction crane and three tons of supplies to the international station. Crippling computer problems keep the astronauts at the outpost an extra day.

Endeavour undocked from the station Sunday, clearing the way for a Soyuz spacecraft carrying two Russian cosmonauts and American millionaire Dennis Tito, the world's first space tourist. The Soyuz crew docked at the station early Monday.

The seven shuttle astronauts spent Monday testing flight control systems and steering jets that will play a key role in their atmospheric reentry and landing.

A cooling system on one of three hydraulic units used to power the shuttle's wing flaps, rudder speedbrake and landing gear was acting up a bit, but Cain said the crew simply would turn it on later than normal to keep it from overheating.

The astronauts also packed up their spaceship, stowing equipment in the mid-deck of the shuttle's crew cabin.

Endeavour has enough fuel and supplies to remain in orbit through Friday.

Onboard with Rominger are three other U.S. astronauts -- Jeff Ashby, Scott Parazynski and John Phillips; Canadian Chris Hadfield; Russian cosmonaut Yuri Lonchakov and Italian crewmate Umberto Guidoni of the European Space Agency.

The crew is the most cosmopolitan ever flown in space, with astronauts from four nations that span three continents on board.