The great blue tube pokes up from a hilltop in Pittsburgh. It is an old telescope, fashioned by hand at the turn of the century. But this humble instrument, sitting under its white-slatted wooden dome, is leading a race that is one of the most exhilarating in all of astronomy.

It is the race to find the first planet in the universe outside our own system.

Most astronomers believe -- with real faith -- that they are out there. Many even believe that the planets out there are inhabited. But still, not on of these unknown shores has been shown to exist.

Now, new instruments being attached to telescopes around the country make it seem certain that within the five to 10 years it takes to do a plant survey, one or more search groups will have discovered the first planets outside our system; or they will have found that we are alone in the universe, more alone than we like to think.

Either way, the results will go beyond simple astronomy. "There is some profound philosophy in this," said one of those beginning the planet search. "The way we think about our place in the universe, the way we think about space when we look up into it at night, the way we think about man's future, all will be changed by the knowledge of what is out there. Or what isn't out there."

George Gatewood, high school dropout, former carpenter, computer tinkerer, astronomer, is director of the Allegheny Observatory of the University of Pittsburgh, where the big blue telescope is leading in the race to find planets.

"I believe we're going to see some planets," Gatewood says. His face is round as a moon, and his expressions of enthusiams are infectious. When planets are detected, he says, we will immediately know several things of importance:

We will know not only what stars the planets orbit, but we will know the size of the planets, and how many major planets are in each of the solar systems that are found. Better, we will know if the new worlds are close enough to their suns to be warm, wet and cogenial to life.

If we want to try to communicate with other beings, we will then know where to look. If we want to send probes to other worlds, we will know where to shoot. And one day, says Gatewood, "I think we will go there. There seems to be no technical barrier to it."

There are groups at Pittsburgh, University of Maryland, MIT, Sproul Observatory, University of Arizona, the University of Califronia and others that are beginning projects to find planetary systems in the universe.

Pittsburgh is somewhat ahead, because Gatewood's group has already built and tested the device necessary to detect planets. Pittsburgh will begin surveying 50 stars next year to see if they habor planet systems. The group at the University of Maryland under Douglas Currie has designed an instrument that will be more accurate than Pittsburgh's, but is a year or two behind in its plans. Other groups are also a few years from "taking data," as scientists call it.

Though astronomers have dreamed about, calculated for and written about other planetary systems for centuries, the first attempt to find them didn't begin until just before World War II. It was then that Peter van de kamp at the Sproul Observatory in Pennsylvania realized that it might be possible to detect planets by what is called astrometrics -- the tracking of extra positions and motions of the stars.

If a star is watched night after night, it can be seen to move slightly. Tracked over years, this movement can be marked as a straight scratch of light in the dark sky. But some stars do not move in a straight line. Instead, their paths make a snake's wavy motion in the sky. The reason the star does not follow a straight path is that it must have an unseen partner. Sometimes the unseen partner is a star pulling it off a straight course by the force of their gravity together. But, theoretically at least, the partner can be a planet.

From the slight wiggle, an astronomer can determine how massive and how near is the unseen companion. If the companion is a star, then the wobble of the tracked star is big enough to be detected even through a small telescope, if logged over some years.

Detecting planets is a different matter.

It requires seeing a wobble less broad than a grain of sand spotted at two miles.

To see such tiny deviations in a star's path, if is necessary to get an extremely exact measurement of a star's position. Unfortunately, when starlight passes through the Earth's atmosphere and strikes the photographic plate of a telescope, it is bounding wildly. For the astronomer it is like looking down an asphalt road on a hot summer day, trying to see tiny, distant figures through the heat waves.

To compensate, astronomers take hunderds of measurements of a star's position. Each measurement may provide a slightly different position, but together they give reliable mathematical depiction of where the star is Ten checks of a star's position will give a more accurate result than one, 100 checks will be much better than 10, and 1,000 will be considerably more precise.

In 1943, using such techniques, Van de Kamp published the first evidence of the existence of a planet. He said he found a planet about six times the size of Jupiter to be orbiting a star called 61 Cygni.Later he added other possible planets to his list, with the clearest case being a planet near Barnard's star -- a particulary close and fast-moving star.

But Van de Kamp's data, taken through the small Sproul telescope, has always been disputed. A few years ago, a defect in the telescope was found to have affected his star-wobble measurements, and the doubt about his planets became even greater.

Gatewood later used the large and more accurate telescope at Allegheny Observatory and another not far away to check such planetary measurements as Van de Kamp's. He took the five most promising planetary systems found up to 1975. All the cases were dubious enough for a general conclusion to emerge among astronomers: no planetary systems beyond our own hve yet been found.

"Then, about four years ago, David Black at NASA called me up," Gatewood says. "He said I had a reputation . . . for wiping out solar systems. He wondered it I could start finding planets instead of wiping them out."

Black was one of the leaders in NASA's effort to organize the search for extraterrestrial intelligence. One of the products of the search was Drake's equation, named after its inventor, Cornell astronomer Frank Drake. d

The equation lists what must be known before gauging the probability of life existing elsewhere in the universe. The first number in the equation refers to the number of stars in the universe, for which a good estimate exists. The second of the seven parts of the equation asks for the number of stars that have planets.

So, any reasonable estimate of life in the universe is stopped until some planets are discovered. With that and some future space missions in mind, NASA four years ago began to encourage planet searches.

The scheme through which Gatewood improved his telescope's powers of discernment was suggested by something Drake said to him about an extraordinarily accurate way of measuring the Earth's movement.

"The idea was no use in itself," Gatewood said. "We didn't want to measure the Earth's motion. But the fantastic accuracy in the idea kept pulling me back to it. I couldn't get it out of my head."

A believer in the notion that the subconscious can consider an idea on its own and produce an answer, Gatewood laid out a problem in his mind just before going to sleep one night in 1976.

When he awoke, the solution was there. "By the time I get around to the foot of the bed, I was deciding whether the idea was any good. As I approached the bedroom door, I decided to go with it until I had a better one. I never reached the door. I turned, wnet to the desk, and wrote it down," Gatewood said.

For years, astronomers had been sitting up nights in their unheated observatories making pictures of stars, taking from a minute up to half-hour to get a single good image. Few could be done in a night. To capture many would take years, so it has been difficult to achieve accuracy in recording star positions.

Gatewood's solution was to eliminate the photographic plate. He put in its place a little electronic system that would register the position and brightness to each star.

Then -- the key to the system -- Gatewood inserted a piece of glass where the telescope eyepiece would be. It is marked alternately with opaque stripes and open glass. The stripes are just wide enough to block the star's image, and the open strips are just wide enough to let it through.

The marked glass moves back and forth across the field of view. This gives the electronic sensors beneath the glass a fresh star image each time the image passes from behind a line into an open space. Now, instead of getting only a few star positions a night, Gatewood's instrument can capture one image every second.

This great increase in the number of measurements improves accuracy many-fold, enough for the old Allegheny telescope to detect planets about Saturn's size or larger.

Sitting in his small office in the observatory, Gatewood appears at first glance more like a banker than a scientist. His gray suit is tidy, his hair is trimmed and slicked. He is talking about competition in science. Now the rivalries tend to be more friendly than fierce. But he recalls that not long ago the logs of each night's observation were kept in code at some observatories, and even now the lists of objects an observatory is looking at will sometimes be locked up as sensitive material. a

In the beginning of this race, there was a chilly moment the first time NASA got several of the competitors together to discuss planet searches. Although information is traded more freely now, the desire to finish first has not vanished.

"Here's the evidence that we are ahead," Gatewood says, grinning. He tosses onto the table a sheet of paper with green grid lines and light pencil marks on it. The graph, from an actual observation, shows that his telescope has the power to detect planets.

Just as Gatewood originially did not intend to go searching for planets, he once had no intention of going into astronomy. He has dropped out of high school, married, and become a carpenter in St. Petersburg, Fla.

But not long after his marriage he bought a small telescope he had admired in a pawn show window."People are too complex," Gatewood says, explaining his career choice. "Stars are easier."

His first telescope led to a bigger one, so often set up in the alley that the neighbors got to pulling down their shades when Gatewood was gazing.

His hobby eventually drew him back tohigh school, to junior college and finally to the University of Pittsburgh for a Ph.D. in astronomy.

At the observatory, turning over and over in his hands a piece of chalk, he explains the importance of finding other planets. "We now have only one example of a solar system. What kind of biology could you have if you had only one clump of plants to look at? So this work of finding planets has some scientific importance."

But he adds that it has imaginative importance as well -- it will change the way we think about the universe and about ourselves. "I think it is possible we will be able to go to these places. There is no technical barrier to it that I can see. We already have conceived systems that might be able to get you there at one-tenth of the speed of light. We could get to some near stars in less than one man's lifetime."

Most trips may turn out to be oneway, because of the large distances. But still, Gatewood says, "I would go. I would get on a ship with some friends, with my wife." He pauses a moment to consider his teen-age daughter. "I think my daughter would go with us."