CAPE CANAVERAL, DEC. 9 -- Columbia's astronauts drained enough fluid from the shuttle's clogged plumbing today to avoid an early return, but forecasts for bad weather at a landing site threatened to shorten the mission anyway.

NASA was going to bring Columbia back to Earth on Monday, a day ahead of schedule, if the constantly rising level of waste water could not be contained or the pipes unplugged.

The astronauts reduced the amount of waste water in the storage tank to slightly more than 3 percent by filling 15 urine collection bags.

That gave the crew a green light for staying in space until Tuesday as far as the water system was concerned, NASA said. But meteorologists were predicting possible rain Tuesday at Edwards Air Force Base, Calif., which could leave the lake-bed runways damp for days.

NASA said it would decide by mid-morning Monday whether to bring the shuttle home Monday night at 9:54 PST.

"That strictly will be based on the weather now," flight director Al Pennington said. "Mother Nature is always the driver."

Columbia's waste water output line clogged when the crew tried unsuccessfully to dump water overboard Saturday. It was the latest in a series of problems to befall the astronomy mission, already hampered by computer failures and pointing trouble with the on-board observatory.

The astronauts used hoses today to suck waste water from a line beneath the crew cabin floor into the urine collection bags. Their initial efforts earlier in the day were unsuccessful.

Fluid splashed onto Guy Gardner's gloves during his first attempt to fill one of the small plastic bags, and astronomer Robert Parker helped him wipe up the mess. The water pressure was reduced for the next try, but the hose became clogged.

Star-gazing by the telescopes in Columbia's open cargo bay continued uninterrupted during the water removal. Among the many targets observed today were a quasar, a powerful generator of radio waves; a white dwarf star with a strong magnetic field, and numerous galaxies.

Scientists and engineers on Earth 218 miles below have been helping the astronauts manage the $150 million mission's three ultraviolet telescopes since an on-board computer overheated and shut down Thursday. The shuttle's only other terminal for operating the instruments failed the day of the launch, Dec. 2.

Ground controllers succeeded today in using the instrument pointing system in the automatic mode, which did not work right during much of the mission. Occasional use of the automatic system, primarily for focusing on faint objects, gave the astronauts a break from having to guide the telescopes manually with a joystick.

"Believe me, we don't mind giving our fingers a rest," said astronaut Jeffrey Hoffman.

Deputy mission scientist Gene Urban said the team was becoming increasingly adept at managing the telescopes.

At the rate the astronauts are going, as many as 160 sources of ultraviolet light and X-rays should be observed by the end of the mission, Urban said.

Before the telescope problems developed, mission planners had hoped to observe about 250 space objects. Because neither ultraviolet light nor X-rays can be seen from Earth, astronomers expect Astro to vastly improve their understanding of hot, violent stars.

Astro's ground-managed X-ray telescope indicated a jet stream of matter zooming this way from a pulsar 3 billion light years away. A pulsar is a star that emits radiation in brief, regular pulses.

NASA scientist Greg Madejski said it was one of the instrument's more exciting findings and timed perfectly: on his birthday. "It was the best gift I could imagine," Madejski said.