With its landing site socked in, NASA ordered space shuttle Endeavour to remain in orbit Friday, delaying the crew's homecoming for an unprecedented third day.

Mission Control said it would guide Endeavour to a touchdown Saturday, on one coast or the other.

It was the first time in 21 years of space shuttle flight that bad weather caused three consecutive days of landing delays.

Friday's postponement added a 14th day to the shuttle mission and a 185th day to the voyage of three returning residents of the international space station.

"We're sorry to tell you that we're going to wave off this attempt for the day," Mission Control told the seven astronauts and cosmonauts aboard Endeavour.

"Thanks for trying," replied shuttle skipper James Wetherbee.

Clouds as low as 500 feet hovered over the Kennedy Space Center and obscured the top of the massive Vehicle Assembly Building, where the spaceshuttles are attached to their boosters.

Forecasters said conditions should improve dramatically by Saturday. Acceptable weather also was predicted for the backup landing site at Edwards Air Force Base in California.

Endeavour has enough fuel and supplies to remain in orbit until Sunday.

Returning space station residents Peggy Whitson, Valery Korzun and Sergei Treschev have been in orbit since June 5. They were replaced by a three-man crew that came up on Endeavour, which also dropped off a new girder.

Also Friday, the leaders of the five space agencies involved in the station met in Tokyo and agreed to try to increase the crew size by 2006 or 2007. Three-member crews are kept too busy with space station repairs and maintenance to conduct much scientific research.

The only way to expand the crew would be to add a second Russian Soyuz lifeboat to the orbiting outpost, at least until NASA's proposed space plane is built.