By Steve Gorman and Alex Dobuzinskis

LOS ANGELES (Reuters) - The search for intelligent life in the universe, at least beyond planet Earth, has been dealt a major blow by government budget constraints.

The world's only radio telescope array specially designed to eavesdrop on potential signals from distant worlds was shut down earlier this month after money ran out, said Seth Shostak, senior astronomer for the group that runs the northern California facility.

The setback comes at a crucial time for the Search for Extraterrestrial Intelligence (SETI) Institute, headquartered in Mountainview, California.

Astronomers there were anticipating a slew of potential new research targets from the dozens of potentially life-supporting "exoplanets" newly detected by NASA's Kepler space telescope to be orbiting distant stars in the Milky Way Galaxy.

"It's a frustrating thing to know that there are worlds out there that may have life, intelligent life, and not be able to look for them," Shostak told Reuters on Thursday.

He said the Kepler telescope has pinpointed about 50 potentially habitable exoplanets in the Milky Way, leading scientists to estimate the existence of at least 500 million such worlds in the galaxy.

The Allen Telescope Array, named for Microsoft Corp co-founder Paul Allen, one of its chief benefactors, consists of 42 dish-like antennas about 20 feet in diameter, operated as one large radio telescope in the Cascade Mountains east of Reading, California.

The site, which stretches across a third of a mile, resembles the fictional array operated by Jodi Foster in the 1997 sci-fi film "Contact," based on the novel by Carl Sagan.

Other radio telescope complexes are capable of searching for extraterrestrial signals in deep space, but only the Allen array was designed specifically for that purpose and was dedicated to that research around the clock, Shostak said.

The instrument is sensitive enough to detect a cell phone call from the surface of Jupiter, if there were one, Shostak said. What scientists are listening for in a galaxy filled with natural and artificial radio "noise" is a distinct, repeating pattern of electromagnetic signals, emanating from space, across a limited range of frequencies.

Built with private donations, and still expanding, the facility is part of the Hat Creek Radio Observatory, run by the the Radio Astronomy Lab of University of California, Berkeley.

But the project was hit hard by recent state budget cuts for UC Berkeley. Money from the National Science Foundation also has been scaled back drastically.

It costs about $1.5 million a year to operate the array, which has been running for five years, and at least $1 million to cover the related cost of the SETI research, according to the institute.

SETI is hoping to gain additional funding support by teaming up with the U.S. Air Force to put the Allen array to work tracking space debris that pose a hazard to satellites, Tom Pierson, the institute's chief executive officer, said in an email notice to financial supporters.

He said the institute also is seeking $5 million in new private donations to cover the cost of a two-year search for radio signals from Kepler-discovered exoplanets.

In the meantime, work goes on at the nonprofit institute, including development of new software systems, new detection algorithms, and additional data storage.

(Editing by Greg McCune)