Astronomers searching for radio signals from intelligent life beyond the Earth say circumstantial evidence is growing that humankind is not alone in the universe.

Reports of the discovery of new planets and of the presence of complex organic chemicals on comets are "encouraging," Michael J. Klein, manager of NASA's radio search for life, said Monday.Research announced at the International Astronomical Union's 20th assembly last week showed the discovery of at least 10 planetlike objects in orbit around distant stars. Other studies showed that comets and cosmic dust particles contain the complex organic compounds that are thought to have been the chemical precursors of life.

"That is the circumstantial evidence that life exists elsewhere," Klein said. "We know now that the materials are there. It gives us a good feeling that we are on the right track."

Klein heads a project called the Search for Extraterrestrial Intelligence, or SETI, which is planning to mount an intensified search for radio signals from civilizations that may exist on planets orbiting distant stars.

Programs run by the National Aeronautics and Space Administration, Harvard University and others have listened for intelligence-directed radio signals for more than 20 years, but only a small fraction of the vast universe and the many radio frequencies that must be monitored actually have been checked.

The Jet Propulsion Laboratory, which is operated by the California Institute of Technology for NASA, has proposed expanding the effort with sophisticated new equipment that would listen to tens of millions of channels at the same time. The equipment would be monitored by a computer capable of identifying signals that could be sent by intelligent life.

Klein said the new equipment would be able to look at 1,000 different stars that are thought to be similar to the Earth's sun, locations that experts believe hold the best chance for the evolution of life.

There also would be "whole sky survey" in many radio frequencies in which every portion of the heavens would be searched systematically.

The new equipment would be 10 million times more thorough than present equipment, he said, noting, "In the first few minutes, we would be able to match all of the searches that were done before."

But even with the new devices, the job is immense, said Frank Drake, chairman of a SETI committee of the astronomical union.

"Many people think the project should succeed in the next year or two," he said. "That's probably not going to happen. The universe is so huge and the cosmic haystack so large, it will take us decades."

The theory behind the SETI work is that because there are billions of galaxies, each with billions of stars, the odds are good that the conditions that permitted life to evolve on Earth also exist elsewhere.

If so, then intelligent life could have developed along the same lines as it did here on Earth. Civilizations that are equal to or more advanced than humankind would be sending out signals, just as occurs on Earth.

Klein said the federal budget now under consideration by Congress includes a $6 million appropriation for the enhanced SETI equipment. He said the total project would last 10 years and cost $90 million.