The Air Force and the National Aeronautics and Space Administration are at war again.

Recently, they clashed over how to share the Majove Desert. Now they're battling over a portion of the microwave spectrum that NASA says is the key to contacting alien intelligences and which the Air Force wants to jam with navigation signals.

A majority of space scientists now say they believe that there are so many stars with planets likely to be able to support life that the odds are good that there is at least one other civilization near enough to ours to detect, to listen to and possibly engage in a dialogue

Many of these scientists say they believe nearby beings may be so many millions of years older and more scientifically advanced than we are that they might hold the secret to our technology survival.

"Stars similar to the sun came into existence 5 billion years before the sun, so if our experience is typical we may have had intelligent societies on distant planets for thousands or even millions of years," said Dr. Robert E. Edelson, director of the search for extra-terrestial intelligence at the Jet Propulsion Laboratory.

"People look at our society and say that in 100 years it will all be gone, so if it's possible for technologies societies to exist for thousands of years we ought to find out how they did it," he said.

The Air Force has not formed a public opinion on that subject, but it has evolved firm plans to orbit 24 satellites in the next eight years which will allow submarines, surface warships, combat aircraft and even foot soldiers to pinpoint their positions on earth. The Pentagon calls them the Global Positioning Satellite, and says 24 are needed to have four over any spot on the earth at all times.

The problem is that the Air Force satellites will broadcast in the same microwave frequencies in which space scientists believe aliens would broadcast if they wanted to be heard. These frequencies range across a band of the microwave spectrum scientists call the "Waterhole." Only in that band to hydrogen and oxygen and you have water, which is why it is called the Waterhole.

Scientists assume that no life exists without water, that no planet populated by intelligent beings or animals thrives without an atmosphere rich in oxygen and heavy with rain.

They also assume that aliens advanced enough to broadcast messages would be at least as familiar with the Waterhole as we are and would choose it for their frequency for the same reasons we would if we were broadcasting. The Waterhole has been described as the "sign language" in which alien civilization might best conduct a dialogue.

The Air Force picked these frequences because they're free of radio interference. Space scientists find the same frequences appealing for the same reasons. Signals from aliens reaching earth free of radio noise will be much easier to detect and identify.

But not for too much longer. The Air Force plans to orbit its first global positioning satellite as early as next year and have its network of 24 in place by 1984. Once the network is in position, it will drown out with its own noise any signals beamed to us from an alien civilization anywhere near its frequencies.

"We're talking about detecting signals that may be infinitesimal in strength by the time they reach earth," JPL's Edelson sadi. "If one of these Pentagon satellites broadcasts its signal down it wipes out the rest of the spectrum where it's broadcasting."

The space agency's strategy in fighting the Air Force is to get a program under way this year that will survey the sky starting next year for alien broadcast signals. The idea is to get evidence for an alien civilization before the Air Force has its 24 satellites in place. If the space agency does that, it might be able to gather public or even world opinion behind a more intensive search.

The space agency has other reasons for making an early search of the sky for alien broadcasts. A consortium of seafaring nations will have an orbit in five years a navigation satellite called Maris at that will overwhelm another portion of the microwave spectrum NASA considers promising. A consortium of countries that make up Intelsat will orbit a new communications satellite about the same time that will take over yet a third.

"It's all going the other way," said Dr. Bruce C. Murray, director of the Jet Propulsion Laboratory. "Talk about protecting these frequencies for sky surveys is like the talk that was heard at the Law of the Sea Conference. Pointless, just anarchy."

Space scientists are deadly serious about searching the sky for alien broadcasts. They say the detection of such signals would be discoveries that would alter the course of human history for centuries to come.

Some astronomers have warned that if alien broadcasts are identified that we should not reply for fear the aliens might attempt to destroy or enslave earth. JPL's Edelson says that if a signal is heard we might decide to spend years or even centuries analyzing the broadcast before the broadcast back.

"That doesn't say we can't learn a great deal by simply detecting a signal and translating what's in it," Edelson said. "The analogy has been made by Phillip Morrison of MIT that we received a great deal in the same oneway sense from the ancient Greeks that we have been unable to transmit back to them."

Another reason the space agency is in a rush to get an alien broadcast survey under way is that it says it can conduct one in five years for no more than $21 million. Mushrooming electronics technology will allow it to build devices called spectrum analyzers that can identify differences between 1 million signals at the same time.

If a space agency cannot get a survey of the sky going from the earth in the next five years it will have to undertake one from earth orbit at some future date, away from the clutter of satellite noise, but one that would cost at least $20 billion. When earth orbit gets too noisy, it will have to move at still more cost to the backside of the moon.

By then it may be too late. Radio transmissions have been radiating away from the earth at the speed of light ever since Mrrconi produced the first one. Assuming he has a good enough tuner and amplifier, it's possible the "I Love Lucy" television broadcasts that have been drifting away from the planet for 20 years and identifying our civilization's level of intelligence have been seen by the real cosmos' version of Darth Vader.