LAS CRUCES, N.M. -- In a wooden dome on a frozen mesa in Arizona, shoulders hunched and shivering in his sheepskin, numb fingers working a telescope by feel in the dark, the young farmer from Kansas discovered the ninth planet, Pluto.

That was in 1930. Now, shoulders hunched with age, he climbs an aluminum ladder wired to the platform of a homemade telescope in his yard to gaze through the desert night at his first and most constant love, the heavens.

In the years between, he has taught Navy and Marine officer candidates in World War II, developed optical tracking systems for Army missiles, surveyed paths to the moon for NASA and started the astronomy department at New Mexico State University here.

He is Clyde W. Tombaugh, who taught himself to be an astronomer and became the first since the 19th century to discover a planet.

At 81, head thrust forward, pale blue eyes aglow, he dashes across town in his white pickup, lunches with colleagues, darts up and down stairs, holds court among stacks of papers in his university office, talks about the mysteries of the universe, and plans for the future.

The discovery of Pluto was one of the top 10 news stories of 1930, and it brought Tombaugh a continuing array of honors. But from the first, some astronomers picked on Pluto's status as a planet.

Only last February, Frank Cooper, director of Burke Baker Planetarium in Houston, wrote that "it seems likely that Pluto will be demoted" to asteroid, a minor planet.

But in May, scientists at NASA's Jet Propulsion Laboratory in Pasadena, Calif., announced that satellite observations show Pluto has a substantial atmosphere. Planets and most moons have gaseous atmospheres. Asteroids do not have atmospheres or moons.

Now Pluto has both a moon, Charon, discovered in 1978, and an atmosphere.

"This latest discovery greatly enhances the stature of Pluto," the announcement said.

Mixing testiness and humor, Tombaugh issued a statement that if Pluto looks like a planet, feels like a planet and smells like a planet, it must be a planet.

In a recent interview he was more blunt. "Yeah, there's a fellow down in Houston who -- I think he wanted to make a noise for himself -- suggested that we should demote Pluto. Well, that just blew the stack, you know. And there was tremendous opposition to the fellow. But that's got cleared up."

It got cleared up when Cooper backed off after the NASA discovery, saying that "if astronomers want to call it a planet, fine . . . . I didn't intend to raise a national controversy." He also said many schoolchildren had written that they didn't want Pluto demoted. Cooper resigned from the planetarium in June.

Tombaugh began studying the stars with mail-order telescopes as a farm boy in Illinois and Kansas.

When he finished high school in Burdett, Kan., in 1925, there was no money for college. He had to stay home and work on the wheat farm.

But he was avid for a more powerful telescope. He made one from directions in a Sunday school newspaper, but the curve of the mirror was askew.

Tombaugh read that mirrors should be ground and tested in a cellar, where the temperature would be constant.

So with pick and shovel he dug one -- 24 feet long by 8 feet wide by 7 feet deep -- while his father, Muron Tombaugh, hired out as a carpenter to pay for concrete to finish it.

Out of that cellar came his first triumph, a 9-inch reflector that would magnify 400 times in diameter or 160,000 times in showing detail.

By now, Tombaugh knew he had to get off the farm. With his new telescope, he made drawings of Jupiter and Mars and sent them to the Lowell Observatory at Flagstaff, Ariz.

He was hired in 1929, sight unseen, as an amateur, to operate a new photographic telescope and try to find a Planet X predicted by Percival Lowell, who had founded the observatory on a 7,250-foot mesa just west of Flagstaff.

Lowell and others had seen perturbations, or wobbles, in the orbits of Uranus and Neptune, as if they were being tugged by the gravity of another planet. In 1915, Lowell predicted a location for Planet X.

Lowell died in 1916, but the search for Planet X went on.

Tombaugh's job called for furnace-stoking as well as star-gazing. He had to shove pine logs the size of railroad ties into the furnace that heated the main building of the observatory. The dome, 300 yards away, where he scanned the skies, could not be heated because the inside temperature had to match the outside or the telescope mirrors would fog.

Tombaugh started working the photographic telescope at Flagstaff on April 6, 1929. He spotted Pluto on Feb. 18, 1930.

The discovery appeared on a blink-microscope comparator, an optical instrument that can show movement of objects in space. It works something like the cartoon booklets children play with. Each page has a figure in a different position. As you flip the pages, the figure seems to move against the background.

Tombaugh saw the movement of Pluto when he blinked photographic plates made on Jan. 23 and Jan. 29. More plates and more blinking confirmed the discovery of a planet moving against the background of the stars beyond Neptune.

The farmer, the amateur, had changed the known universe at age 24.

But Tombaugh and other astronomers concluded that Pluto, although a planet, was not Lowell's Planet X. The new planet was 6 degrees from its predicted place and 10 times dimmer than the predicted planet. It was too small to cause the wobbling of Uranus and Neptune.

Tombaugh spent 13 more years searching for Planet X.

"There is no Planet X," he says now, then pauses: "No, I'm not prepared to say there are no more planets -- only to the limit of my plates."

Soon after the end of World War II, in which Tombaugh instructed officer candidates, the Army hired him to direct its optical tracking of missiles at White Sands Missile Range in southern New Mexico. He said he had some close calls.

In one of them, a V2 rocket misfired and plummeted back. "It missed one camera station by less than 100 yards. From 100 miles, four tons of metal, pal, and it made a crater 75 feet wide and 75 feet deep. I was just petrified."

Tombaugh lives in a white stucco ranch-style house shaded by tall pecan trees. A 5-foot, glass-fronted case and the fireplace mantel in his living room are filled with medals and citations from the Royal Astronomical Society of Britain, other professional societies, NASA, White Sands and several universities. He is a member of the Space Hall of Fame at Alamogordo, N.M., and the White Sands Hall of Fame. He has bachelor's and master's degrees from the University of Kansas.

The farm telescope that won him his job at Flagstaff is mounted in his yard on a chassis made of spare parts: the base of a cream separator, the shaft of a 1910 Buick, rods and gears from a straw spreader and a steam engine.

A smaller telescope rests in a wooden cabinet.

A third, the one Tombaugh uses for serious observing, an 11-inch reflector supported by a red steel frame, rears up 20 feet.

Patsy, his wife of 53 years, treats him like any veteran spouse.

Coming into the yard to offer iced tea as Tombaugh explained his tall telescope, she offered a comment.

"Clyde," she said, "that frame needs painting."

"Yeah, you're right," he said. "I haven't painted it since I built it 25 years ago. I'll have to get to that."

But Tombaugh had a higher priority for work on that telescope. He planned to grind a convex mirror that will reflect images down from the viewing platform, 15 feet above the ground, to a concave mirror at the base platform.

Then he won't have to climb the aluminum ladder as he persists in pursuit of the first of his own Ten Commandments for Planet Hunters:

"Behold the heavens and the great vastness thereof, for a planet could be anywhere therein."