The Columbia astronauts might end their glitch-plagued astronomy flight Monday, one day early, because of a clogged line keeping them from flushing the contents of the ship's septic tank into space, officials said Saturday.

"The plumbing's stopped up and there is no Roto-Rooter," chief flight director Randy Stone told reporters.Flight director Granvil Pennington said late Saturday the mission would last at least nine days, which would result in a landing Monday, and if work to find additional storage space for the shuttle's waste water is successful, the astronauts could get in a full-duration 10-day flight.

"We can guarantee you wastewater capability of nine days," astronaut Story Musgrave radioed the crew from mission control in Houston. "We might be able to get you out to a 10 (day) mission. But right now we're guaranteeing, in terms of waste water, a nine (day mission)."

"Well, Story, we appreciate you guys working so hard getting us the full mission," replied astronaut John "Mike" Lounge.

Landing originally was scheduled at 10:46 p.m. MST Tuesday at Edwards Air Force Base, Calif. Bringing the crew home a day early would result in a landing at 10:53 p.m. MST Monday.

Material already in the shuttle's waste storage tank was flushed into a rubber bag in the crew module and Columbia's seven astronauts were ordered to stop using the ship's toilet.

After working around two failed computers, a broken data recorder and problems getting a $50 million telescope pointing system up and running, the "Astro-1" astronomy mission was finally in high gear when the wastewater problem cropped up Saturday.

Project officials said the astronauts were on track to have observed 160 to 170 of a planned 200 targets in a full-duration 10-day mission. Despite the threat of an early end to the 38th shuttle mission, astronomers on Earth were understanding.

"We feel now things are going very well and we would be very disappointed (about an early landing)," said astronomer Warren Moos. "But if there's something that endangers the spacecraft, there's simply no choice."