A telescope array in California built to listen for signals from distant alien civilizations has been shut down for lack of money, its operators say.

The Allen Telescope Array has been put into "hibernation," its operators said, and "starting this week, the equipment is unavailable for normal observations and is being maintained in a safe state by a significantly reduced staff."

The announcement came Friday in a letter to donors from Tom Person, chief executive officer of the SETI Institute in Mountain View, Calif., ScientificAmerican.com reported.

The ATA is a partnership between the SETI Institute, which built the telescope array, and the University of California, Berkeley, which is responsible for operating it.

The non-profit SETI Institute, founded in 1984, relies mostly on private donations to support its research.

A number of early SETI Institute projects had been funded by NASA, but Congress stopped NASA's short-lived SETI program in 1993.

The SETI Institute has been working for more than two years to find new funding, Person said, and has even offered ATA's services to the U.S. Air Force to assist in tracking orbital debris that can endanger defense satellites.

"We are continuing discussions with the USAF and remain hopeful that this effort will help provide future operating funds," he wrote in the letter.

ATA operations cost about $1.5 million per year, Pierson said.