The shuttle Columbia, whose six-day-old astronomy mission has encountered more perils than Pauline, yesterday ran afoul of a clogged plumbing line that may force NASA to shorten the flight by a day.

Other NASA scientists had reason to celebrate, however. Whizzing toward Earth from the East, high above Columbia as it approached the coast of Chile, was another NASA spacecraft: the nuclear-powered Galileo probe bound for Jupiter, furiously sending back snapshots of the home planet and its moon.

"Galileo today became the first confirmed interplanetary visitor to Earth," said project manager William O'Neil. Since the craft left Earth 14 months ago, it has traveled around Venus. This was the first of two "Earth encounters" planned on its six-year voyage to Jupiter, the most complex interplanetary journey ever flown.

At its closest approach to Earth, at about 3:35 p.m., the craft "hit our target within five miles and our arrival time within one-half second. That's not bad," O'Neil said.

Galileo performed so well that the recorded data was available faster and sharper than expected, the scientists said. By 5:30 p.m. they were viewing on their television screens images of the moon and Earth, the latter less than 30 minutes old.

Galileo is sending back to its makers at the Jet Propulsion Laboratory several day's worth of data on the Earth-moon system after picking up a gravity assist from its home planet that boosted its speed by 11,600 mph relative to the sun -- to about 81,000 mph by late yesterday.

The craft is expected to yield unprecedented views of never-before-seen parts of the moon, new perspectives on the Earth, insight into the impact of greenhouse gases, the planet's magnetic field and other aspects of the blue planet. Most of the recorded information will take a few days to play back and analyze, scientists said.

Galileo's 25 hours of unique sightseeing will also be made into a movie of the spinning Earth.

Scientists noted that its trajectory at one point coincided with the one Christopher Columbus took on his journey to the New World, but Galileo went the same distance in about eight minutes. The spacecraft took about 12 hours to get from the moon's orbit to Earth, a trip that took the Apollo astronauts 72 hours.

As Galileo sped toward the asteroid belt, however, scientists working on Columbia's Astro-1 mission coped with the latest in a series of setbacks. Just as they were swinging into normal operations after overcoming the technical demons that had plagued their $150 million observatory, early yesterday morning crew members discovered that lines designed to carry waste water from the shuttle and dump it into space had become clogged.

Mission managers said it is likely the flight will have to land Monday night instead of Tuesday night as planned. But the crew and ground teams were trying to come up with a way to fix the plumbing system.

The lines are designed to remove both human and mechanical waste liquids from a tank in the orbiter. While some of the seven-member crew engaged in scientific endeavers, others tried to clear the unknown obstruction with a burst of air. Their efforts were in vain.

"The plumbing's stopped up and there is no Roto Rooter," said flight director Randy Stone.

As a result, the astronauts were asked to change their bathroom habits, among other things.

"To preserve all the waste water volume that we have, we'd like you to use the male UCDs {urine collector devices}. . . . You've got 54 of them," Story Musgrave at Mission Control radioed the crew. The devices -- large rubber bags that are shaped like balloons, officials said -- can be sealed and stored inside the shuttle.

"We do recommend using each bag as often as you think is reasonable to fill the bag up," he said.

Astronaut Mike Lounge at one point hooked up a much bigger rubber bag -- kept on board for just such purposes -- to transfer about 95 pounds of waste from the plugged up storage tank -- which was about two-thirds full and would be at full capacity within 20 hours.

Emptying that waste might add another 40 hours of flight time, but that was not enough. NASA requires two days of leeway in case of bad weather or other problems with landing, officials said.

The crew later recommended also trying to use empty drink bags to store liquid waste.

The scientists tried to adjust once again to the latest letdown in a flight that was delayed for six months and then faced serious problems trying to aim the telescopes.

"We would be disappointed" if the mission is shortened, said Warren Moos of the Johns Hopkins University telescope team. "But we understand that's the way a mission works."

Meanwhile, he said, using Astro's ultraviolet telescopes, he had "nailed" some new information on Jupiter's moon Io that scientists had long sought.

"We've had one problem after the next . . . we've worked around {them}. I guess the word is the 'can-do' attitude associated with NASA. I think we're seeing it."