If there are any intelligent beings in outer space beaming radio signals to Earth, they'd better be sure the message gets here by Oct. 1.

Among the dozens of federal programs scheduled to plunge into oblivion that day--the first under the new, austere fiscal 1982 budget--is one of the most exotic and ambitious endeavors the government has undertaken: The National Aeronautic and Space Administration's Search for Extra Terrestrial Intelligence. It is the chief hope for discovering whether there is intelligent life elsewhere in the universe.

The search--known in government circles by its acronym, SETI--is a six-year-old effort to develop antennae and computer programs that could discern "non-random sound events" from the flood of radio signals constantly flowing toward Earth from all corners of the cosmos.

As NASA planned it, receivers at the Deep Space Network facility in Goldstone, Calif., would conduct an "all sky, all frequency" search of radio transmissions. The computer would search the signals for patterns, which could indicate that the signals are generated by intelligent sources.

"What we are trying to do here is answer an important question--whether human beings are alone in the universe," said NASA spokesman Charles Redman. Cancellation now is particularly painful, Redman said, because NASA's engineers are within one year of completing the computer programs needed to sort out intelligent patterns, if any, in the "cosmic noise."

Actually, the SETI program has been living on borrowed time for three years, ever since it won one of the bureaucracy's least favorite distinctions: the "Golden Fleece" award presented by Sen. William Proxmire (D-Wis.).

After Proxmire attacked the program ("It is hard enough to find intelligent life right here in Washington," he said), it was cut from NASA's annual appropriation bill.

But the space agency, displaying some budgetary intelligence of its own, quietly transferred SETI to its "exobiology" program and continued to fund the search. In each of the past three years, NASA has spent about $1 million on the search for extraterrestrial intelligence.

Proxmire struck again this summer. Choosing a moment when Sen. Harrison H. Schmitt (R-N.M.), a former astronaut and strong NASA supporter, was off the Senate floor, Proxmire won voice-vote passage of an amendment deleting all funds for SETI. The administration, reluctant to fight congressional budget-cutting intitiatives, went along, and House-Senate conferees adopted Proxmire's amendment.

The result--when Congress approves the conferees' bill--will be one more dead program and many hard feelings at the space agency. A NASA official noted that during the Senate debate, Proxmire made this observation: "There is not a scintilla of evidence that intelligent life exists beyond our solar system."

To which the NASA man ripostes: "As late as 1491, there was not a scintilla of evidence that America existed, either."