SETI probes focus on microwave frequencies ("the quietest radio band in nature everywhere," according to Arnold) and seek out narrow band emissions that the scientists believe may have been artificially produced. As Arnold sees it, these signals could be anything from "leakage from a radio transmitter, which simply tells us that at one point there was a culture that used radar... to full-blown wide and band universal television."

Some searchers, including Horowitz, have suggested that there are "magic frequencies," common frequencies which would be likely to be used by extraterrestrials eager to communicate. One of these is 1420 megahertz, which is the neutral hydrogen frequency. As Arnold explains, "No matter where you are in the universe, you'll know about hydrogen. Even if you have four eyes."

SETI scientists are firm in their belief that inter travel is practically preposterous. Arnold says that UFO search is "an entertainment industry... a diversion. Although he concedes that "it's good in that it gets people thinking," he is alarmed by "the claims people are willing to accept without evidence. Lack of critical thinking... that's what upsets us about the area."

SETI's second assumption--that intelligent beings would definitely opt for radio transmission as medium--is where Frank Tippler disagrees.

"If they existed, they'd be here," he "Interstellar travel isn't that hard."

Especially for civilizations that, according to his culations about the age of the universe, probably a huge jump on Earth's technology. "If our evolution is typical, then most of the civilizations have already formed on billion years ago. That's lot of advance

Tippler gives examples of the types of revolution technology, not very far from being created on Earth, that would allow aliens to visit Earth with relative. He says that NASA had a conference about 10 ago that asserted that the development of self-replicating robots may only be 50 years in the future. These machines would use materials from foreign solar systems to "reproduce," and would thus remove barriers presented by interstellar distances.

These distances, of course, would be shortened more by inevitable advances in rocket technology as nuclear pulse rockets, which have been studied recently by the British Astronomical Society. Tippler describes these as, "roughly speaking, rockets which have hydrogen bombs dropped out the rear instead of chemical fuel."

With these rockets, Tippler suggests, it would take a craft only 10 million years to cover that whole galaxy. He believes that a civilization with millions of year additional progress could get here even faster than that. And, he adds, he finds it "hard to imagine that they'd come here and not set up a permanent base... I'd expect their presence to be very obvious if in they were here."

Tippler uses these examples, along with an evolutionary, argument that has been forwarded by Er. Mayr, a retired Harvard zoology professor, to fight allocation of funds of programs like SETI.

But the same type of conjecture is commonly us to support UFO research. An MIT professor also believes that advanced societies would have the capability to visit Earth.

"The usual scientific view is that because it's much easier to listen than to travel, we should look radio... but we should also look at the flip side. If you were trying to find out about an alien society, would you prefer to ask them the truth, or would you spy on them? Of course, you'd spy on them."

As he sees it, spying is preferable to radio communication "100 to 1," because it allows the visiting intelligence to collect information about non-technological species (which SETI does not) and it supplies military advantage, should that be necessary. Like Tippler, he discredits the SETI advocates' notion that cost and difficulty would keep extraterrestrials from visiting Earth, citing the same technological advances.

"In looking for radio, we're assuming they're stillstuck with radio... There's a lot of effort being put into listening, but no one's putting any effort into looking for them here."

Almost no one, that is, within "respectable" scientific circles. But the search for extraterrestrial visitors here on earth, popular since the late, Forties, continues fullforce. And it's not just limited to the National Enquirer.