Lunar Prospector's collision with the moon yesterday morning left no visible cloud of dust, but researchers still hope to find traces of water in a vapor plume possibly created by the impact.

At least 20 observatory telescopes focused on the moon's south pole as the spacecraft, in its final task for science, dived toward a frozen crater and smashed itself there around 5:52 a.m.

Experts hoped the fire and violence of the collision, unseen from Earth, would vaporize ice thought to exist in the shaded crater and send a wet plume, detectable by special instruments, spiraling into the lunar sky.

Edwin S. Barker of the University of Texas McDonald Observatory, a lead researcher in the project, said telescopes equipped with ultraviolet detectors took hours of data following the impact, searching for the chemical signature of water.

"It's really too early to draw any conclusions," Barker said. "So far, we haven't seen anything that says water or anything else."

Large stores of ice on the moon would make it much easier and cheaper to establish a base there, or to use the moon as a way station to more distant bodies.

Water can be broken down chemically into hydrogen and oxygen that can propel a rocket or power generators. Oxygen also would provide a breathable atmosphere for lunar explorers.

Lunar Prospector was scheduled to end its mission yesterday, and scientists running the $63 million project decided smashing the craft into the moon in search for water was a fitting end.

Prospector was launched Jan. 6, 1998, and spent about 18 months in lunar orbit, using five instruments to map the magnetic, chemical and gravitational character of the moon.

One instrument received a signal for hydrogen, leading scientists to suggest there was frozen water in the deep, constantly shaded craters around the lunar poles. By some estimates, the could be as much as 300 million metric tons of ice in the frozen lunar soil.

Officials of the Association of Lunar and Planetary Observers encouraged amateur astronomers to focus telescopes on the moon and report any signs of Prospector's impact.

Despite the lack of obvious evidence, officials said Lunar Prospector appeared to have smashed into the moon.

"We have every reason to believe it made it to the impact site," said David Folta, the Goddard Space Flight Center engineer who gave the final guidance signals to Prospector. He said the spacecraft received the signals and was operating normally when it disappeared behind the moon, where it was to ignite its rockets.

Had the rocket firing failed, said Folta, the craft would have reappeared in orbit, still sending out radio signals. Instead, there was only silence.