WHEN Gordon Barnes signed on as Channel 9's weatherman in the fall of 1976, he promptly was dispatched to the Capitol steps to predict the weather for the upcoming Carter inauguration. It was pouring that day, but Barnes was undaunted.He issued his prediction, live, standing under an umbrella in the pouring rain. Partly sunny, windy and cold, he promised his viewers, with temperatures in the low 30s.

It was a nearly perfect prediction, and it will be a cold day in July before Barnes lets anyone forget it.

In fact, in the six years since he's come to Washington's top-rated Channel 9 (he was hired to fill the galoshes left vacant by the death of weatherman Louis Allen), Barnes has made his reputation as a long-range forecaster. Ask him to pick a sunny Sunday for a wedding next April and -- often for a fee -- Barnes will do it. Long-range forecasts, he said recently on CBS' "Morning" show, "are my forte."

And that's why, after six years on Washington TV, seemingly nonstop radio broadcasts and a bustling private weather consulting business, Barnes has become the forecaster many other forecasters love to hate.According to one of his critics, it takes only the mention of Barnes' name at a cocktail party where local meteorologists are gathered for black clouds, big black clouds, to form. His long-range predictions particularly irritate his critics.

"The man is in show business," says Ross LaPorte, the meteorologist in charge of the National Weather Service's Washington-area forecast office. "He's trying to sell a product."

"If he can make a long-range forecast as accurately as he can make a dry martini, he's dynamite," jokes NBC's Willard Scott, the ex-Washington weather watcher. "I personally think long-range forecasting is about as valid as a warranty on a used camel."

The American Meteorological Association and the National Weather Service agree. They put the upper limit on accurate predictions of daily weather events at about 10 days. And while the National Weather Service issues monthly and seasonal "outlooks," it regards anything more specific with ill-concealed disdain. Anything more long-range than that, it says, is guesswork, and one would do just as well to consult an almanac for climatological averages.

But Barnes, 49, calm and crisp in the Ultrasuede blazers he favors, chalks up a good part of the criticism to the envy of desk-bound bureaucrats who secretly yearn for the white-hot television lights. "If they think they can do a better job, why don't they apply for my job?"

His job, he says, is to predict. Some examples of the forecasts that have both peeved and pleased his viewers and private clients:

In 1977, the Minnesota Vikings hired him to predict conditions for a playoff game against the Rams in Los Angeles. Rain, Barnes told them. Rain before, rain after, rain during. Find us a rainy place to practice the week before, Viking management responded. "Tuscon," Barnes told them. The Vikings went, they sloshed, they conquered, 14-7.

In that same year, the Fairfax County Water Authority paid Barnes $3,000 to tell it when and whether the reservoir was going to fill. Barnes made predictions for two time periods. "One was 100 percent right," says a water authority spokesman. The other was "pretty far off."

For this summer's royal wedding, Barnes predicted sunny but cool weather in a network telecast four months before the event. He wasn't too far off, but his critics say it isn't too hard to predict London weather at that time of year.

"My judges are my viewers, my clients and my management," says Barnes. "If they're satisfied, then I have to figure I'm doing a good job."

"Predicting football weather?" complains Helmut Landsberg, professor emeritus of meteorology at the University of Maryland. "It's astrology. I'm sorry, but I put it in the same category."

"What people don't realize is that there's a lot of mumbo jumbo in this business," says NBC's longtime weatherman Fred Field."Alan King calls me up and says, 'What's the weather going to be like the second week of May?' Well, how the hell should I know? I could give him an exact forecast and charge him $1,000, but [there are] those of us in the business who . . . refuse." Working Up a Storm

Barnes rips through the day like a tornado. He works five days a week now instead of his once habitual seven, a moderation following two months' hospitalization last year for a gall bladder ailment and complications. But his workday routine still reads like a flextime bureaucrat's nightmare.

At exactly eight minutes after 5 on a recent afternoon, Barnes is sitting on the edge of his chair behind a metal desk in his small office at WDVM. The 5:30 television news is nearing. But before that there are radio spots to make -- he does 84 of them daily along with his six TV forecasts. His eyes dart to a digital clock radio on his desk. He glances at a fistful of papers, then at a radar weather screen. He waits.

He's managed this pace, off and on, since about 4:30 a.m., when he began reading weather maps and doing local weather reports for radio stations in Frederick, Md.; Roanoke, and Charlottesville, Va.; Duluth, Minn., and Fargo, N.D., as well as WTOP. When Barnes got the nod from the executives at CBS' "Morning" show last year, he decided to stay on at Channel 9, and keep most of the radio work, too. It's simply a matter of being organized, he says.

A career in television news can be as nerve-racking as walking a tightrope; in fact, Barnes was fired from WCBS in New York before he came here. But now, with his radio forecasting and outside business, Gordon Barnes has made his safety net long and wide. Even with a new five-year contract at WDVM-TV, which he will describe only as "very acceptable," and a two-year contract with CBS-TV's "Morning." (His agent is Richard Liebner, who's known for speaking softly at negotiations but carrying away a big contract for the likes of Dan Rather, Mike Wallace and others.)

Seated at his desk, Barnes feeds WTOP one 30-second spot. Then another, then the third, all of which will be broadcast throughout the evening. The digital flaps on his little white clock keep dropping as he talks. He's watching them and ad libbing at the same time.

"And this evening," he finishes, "the nighttime low will be Thursday." Pause. The nighttime low will be Thursday ? "Whoooops." He starts over.

A machine in the next room buzzes. Barnes looks up from the radio microphone. "Would you turn off that teletype," he askes his wife, Clarissa, who's seated nearby. She does, quickly.

Time for the 5:30 TV news. He races out of the office down to the studio.

Barnes bumps into sportscaster Glenn Brenner in a small room off the studio. Brenner is rocking back on his heels, holding his hands over his ears. Barnes checks the time, and sees he's got a few moments for some banter.

"How are your sinuses?" Barnes asks him, already knowing.

"Hey, when's this weather going to change?" says Brenner, rocking back and forth on his heels. Two millionaires, shooting the breeze. "I feel like I've got two hockey sticks shoved up my nose."

"We're going to have this weather for another two days," Barnes tells him, withe undisguised glee.

"I can always count on you, Gordon," says Brenner.

Barnes meets anchorwoman Maureen Bunyan in the elevator. "Hi, babe," says Barnes. "Hello," says Bunyan. "You look so handsome." They lean toward each other in the dim light and, descending, trade a celebrity kiss, the cheek-to-cheek kind that doesn't muss the makeup. Helpmate and Admirer

Clarissa Barnes is still up in his office. It's the second marriage for both of them. At 33, brown-haired and wide-eyed, she's yound enough to remember watching Gordon Barnes on TV in New York, as a teen-ager growing up in White Plains.

Though she met Barnes while working as a news announcer at WTOP radio (she was Clarissa Douglas), and then went on to Mutual, she quit her job after they married in 1978. "He's the consummate gentleman," she says of her husband. "Considering he's a 'celebrity,' he's the nicest guy in the world.

"I enjoyed my job," she says, smoothing her jean skirt. "I was good at it. But it's more important to me right now to try to be with him. I try to keep his hours."

That means getting up with him every day at 4:30 at their McLean home, making the coffee and feeding the cats, two Siamese named Partly Cloudy and Mostly Sunny, while Barnes fiddles with his forecasts, and then doing chores around the house until he gets home, around 11 a.m., for his midday nap. She takes a nap, too.

Post-nap, Barnes heads back to WDVM. Clarissa plays "raquetball or something," and waits for her husband to come home for supper. They have two hours then before he heads back to the station at 10 to do the 11 o'clock news.That's when she telecopies the maps for the next day's "Morning" show to a CBS artist in New York.

They think of themselves as homebodies, but that may be only in the Washington sense of the word, where fewer than five invitations a week can drive socially aware couples to unmitigated anguish. Her racquetball partner is a congressional wife, and they get invited to James J. Kilpatrick's farm, and Barnes mentions that Walter Cronkite calls him up "at least three times a year" for maritime weather reports. Elizabeth Drew knows him well enough to call up and request a forecast for her recent Bermuda honeymoon.

From his home, Barnes runs the private side of his weather empire. He operates the Barnes Weather Service in a paneled and cork-lined basement office. The service is not listed in the phone book, but Barnes has at least half a dozen clients, including food processing and shipping companies, and commodities traders trying to decide how to make hefty profits on next year's crops. He says his rates for long-range forecasts start at $2,000 and can go as high as $50,000. He's also paid by the Justice Department from time to time to testify as their expert witness in air crash cases where weather is a factor. The Krick Influence

The Barnes system, he says, is based on a system developed at Cal Tech in the 1940s by meteorologist Irving Krick. If Barnes' name produces an uproar among meteorologists, Krick's whips up hurrican winds. Krick claims to be abel to predict daily weather events to the year 1985. And a Krick associate says they'll soon have all the weather worked out through the year 2000.

But Krick's claims are viewed with skepticism by some in the scientific community. In the '70s, a National Academy of Sciences panel investigating long-range forecasting methods asked Krick to participate in a verification test. Krick declined.

In the Krick system, weather moves across the country in six-day cycles. Barnes has maps for about 85 such cycles, which he keeps in a ring binder at Channel 9. The trick, Barnes says, is to advance those six-day cycles indefinitely, in the right order.

"It's very complicated," says Barnes, who claims to have learned the Krick method years ago when he worked for Krick as a weather service salesman. "There are only three of us who know it, and it's not written down. My wife worries what would happen if, God forbid, all three of us went at the same time."

A more recent study published in the "Bulletin of the American Meteorological Society" found Krick's long-range results to be no more accurate than random climatological predictions.

That doesn't necessarily reflect badly on Barnes, though, because Krick says Barnes doesn't know much about the system anyway. "He's tried to learn some of our techniques," says Krick, from California, "but he's not privy to our [current] information."

Barnes' critics like to point out that he has never sought the seal of approval that the American Meteorological Society grants to broadcast meteorologists. Barnes points out that he's a member of the American Meteorological Society, and as for the seal, he has never even considered it. "Why should I need to verify my weather with anyone else?" Bermuda High

Barnes backed into his weather career, by joining Pan American Airways after high school in his native Bermuda. While training with Pan Am in New York, he also took university correspondence courses in math, physics and meteorology.

By the time he left Pan Am he was operations manager for all of West Africa. He came back to the States and took a series of private forecasting jobs for construction and retail companies. He forecast frost for Florida department stores that wanted to be sure to get their anti-freeze ads out on time. Eventually, Barnes wound up as a weekend weatherman for a Tampa television station.

From there, he went to WCBS-TV in New York for 6 1/2 years."They took a survey and I was told I wasn't attracting enough female viewers," he says, explaining his dismissal.

To critics who feel his long-range forecasts may have been a factor, Barnes says, "It wasn't the long-range forecasts and I can prove it." The station management backs him up. "I really can't recall why he was fired," says Rober Hosking, then the station general manager and now president of CBS Radio. "I can't believe it would have been for that. We were last in the ratings at that time, and when you're dead last you make changes. Gordon Barnes was one of them."

After he was sacked, Barnes expanded his radio work, including weather spots for WMAL and WTOP radio here, and kept up his private clients. When Channel 9's Louis Allen died in May 1976, Barnes was ready.

Washington, he says, was a very pleasant surprise. "Washingtonians are much more diplomatic. In New York it got so I couldn't go out for a meal without someonw coming up and saying 'Goddamn you, Gordon Barnes, I though you said it wasn't going to rain, and it rained all over my picnic!'"

Still, Barnes has continued so stir controversy since he left Gotham for the capital's humid shores. In 1977, he called the National Weather Service "incompetent." This moved a few government meteorologists to fire off angry letters to the ethics committee of the Meteorological Society. But nothing much came of it. "Barnes' response to our letter was somewhat noncommittal about future behavior," recalls the eithics committee chairman.

A University of Maryland meteorology professor, Alan Robock, sent a similar letter of protest to the committee this year, complaining about Barnes' long-range forecasts. Robock said Barnes' claims raise public expectations that meteorology can't fulfill.

In addition, one of Robock's graduate students, now a research meteorologist at the National Aeronautics and Space Administration, checked a 1979 Barnes' weather almanac of long-range predictions. There were no better than predictions based on the 30-year climatological average, according to Robock.

Others, though, count on Barnes. "His predictions have been right on the mark," says Curt Barlow. A local photographer who pilots his Cessna down to the Bahamas each year, Barlow has relied on Barnes' predictions for the past two years. Though Barnes updated his initial October forecast a week before Barlow's trip each January, Barlow says the only change was to shift the entire forecast ahead one day. And Barnes didn't charge him a dime.

But the National Weather Service shies away from forecasting that specifically that far in advance. In fact, a Weather Service study in which six forecasters were asked to predict the average temperature for a week one month in advance showed little or no acceptable skill, according to Don Gilman, director of long-range forecasting for the Weather Service.

Barnes claims 80 percent accuracy no his long-range predictions. In contrast, the National Weather Service claims 65 percent accuracy for its monthly and seasonal temperature forecasts, and for rainfall about 55 percent. "Is he using the same verification standards we are?" asks the Weather Service's Ross LaPorte.

"He's never published his methods," says Maryland professor emeritus Helmut Landsberg.

"Look," Barnes counters, "if you have something that works for you, are you going to give it away?"