Titan, the smoggy, haze-shrouded moon of the planet Saturn, bears a pitted surface marked by lakes or even seas of liquid organic chemicals, astronomers have discovered in radar signals received by the world's largest radio telescope.

The giant Saturnian moon also holds evidence of water in the form of ice. Some scientists are speculating that although Titan is deeply frozen now, crashing comets or asteroid-like objects could have dug deep craters millions of years ago and heated the surface briefly -- at least long enough for the first "prebiologic" chemicals to start forming there.

In a report published online today by the journal Science, Donald B. Campbell of Cornell University and his colleagues describe how they used the 1, 000-foot-wide radio telescope at Arecibo in Puerto Rico to bounce radar pulses off Titan's surface and determined that the moon must be covered by lakes of hydrocarbons.

Earlier studies, obscured by Titan's thick nitrogen atmosphere that is choked with clouds of methane, suggested that the entire moon could be covered by an ocean of tarry hydrocarbons many miles deep.

But the new observations from Arecibo, as well as those from a new radio telescope at Green Bank, W. Va., have changed that idea completely; they have detected lakes of organic compounds that are liquid enough to reflect glints of radio waves like the glints of light shining from lakes on Earth.

By far the largest planetary moon in the solar system, Titan is 3,600 miles in diameter and orbits brilliant, ringed Saturn from an average distance of 760,000 miles away. The planet has 30 other known moons -- but all of those are far smaller.

Even though Titan's surface apparently holds organic chemicals and water -- albeit frozen solid as ice at nearly 400 degrees below zero -- there is little possibility that life of any kind exists there now, and probably not even in the past, most scientists agree.

But the moon may well have once experienced violent volcanic eruptions or enormous impacts from comets that could have warmed parts of the surface enough to mix the organic compounds with liquid water and thereby start the chemical activity that in more benign climates on Earth has led to life.

"It's all highly speculative," Caitlin Griffiths, a planetary atmosphere specialist at the University of Arizona said in an interview. "But that's why we want to go there and look for hard evidence."

In a commentary on the Cornell team's radar observations, also published online by Science, Ralph Lorenz of the University of Arizona suggests that there may be as many as 80 such lakes ranging from 30 to 100 miles across, and probably thousands of much smaller ones.