The night seemed made for great expectations, a coincidence of perfect timing that hours earlier had found the city getting the long-awaited go-ahead on a new convention center.

Gathered together as if in triumph was the prestigious, by-invitation-only 100-member Federal City Council whose ranks include business leaders like Sol Linowitz, Mandell Ourisman, Roger L. Stevens, and James T. Lynn, the new president and last night's guest of honor.

"I think it's the greatest thing that could have happened to Washington," said an exuberant Marshall Coyne, owner of the Madison and Dolley Madison Hotels and one of the proposed center's staunchest supporters.

The Jockey Club had been rearranged buffet-fashion and the tables heavily laden. The bar was doing a brisk business.

To one side stood the evening's host, one John Bennett Coleman who has been introducing himself and his refurbished hotel in a series of get-acquainted parties, sparkling questions from many getting to know him.

One of them at a party a few nights ago, was Ethel Kennedy. Coleman had given a luncheon for everyone at her pro-celebrity tennis tournament this summer. Still, the question remained about the private person behind the public persona: "Who is he?" she asked.

John Bennett Coleman is rich, successful, shrewd, aloof, restrained, serious, extravagant, generous, brusque, wary and secretive. He is also the new owner of The Fairfax Hotel.

That in itself might be sufficient reason to take notice. Washington society, unlike New York society, somehow manages to get along without a supper club to call its own but it is always on the lookout for one. Rumours abount, for instance, that Coleman has persuaded Annabel's, the fashionable London nightclub, to open an "annex" at The Fairfax.

For a dozen or more years, about the closest thing Washington had to a supper club with class was The Fairfax's Jockey Club, a once-chic hangout of famished overachievers which began losing customers a couple of years ago.

Now it is back in business, courtesy of Coleman, the 43-year-old multimillionaire Chicago investment tycoon whose purchase last fall of The Fairfax signaled his arrival on the Washington scene. It was an event calculated to attract attention for more reasons than his reported $60 million.

The way some people see it, there hasn't been much out-of-town money like Coleman's dolling up a midtown business like The Fairfax, and expectations are high.

Coleman has made no secret of the fact that he sees this "company" town ripe for chucking its wearisome image of provincialism, ripe to blossom forth as an epicenter of international commerce and trade. Concorde enhances the potential.

"Suddenly Washington is interested in more than government and the media," says his friend Joan Braden, who seems a little surprised (though not disagreeably) that "business is frightfully acceptable today" among fellow card-carrying liberals.

Coleman bought The Fairfax a year ago from Col. H. Grady Gore, 83, the retired millionaire Maryland realtor and politician whose family had owned it since the 1930s. The purchase price was somewhat less than $6 million and subsequent refurbishing of its 180 rooms cost a little more than $5 million.

Even then the Coleman touch made money, marvels Ann Milligan Gray, the Chicago decorator whose husband John, president of Hart, Schaffner and Marx, is one of Coleman's best friends.

He ordered 1,600 yards of $46-a-yard carpeting from England on a Thursday, received price confirmation on Friday and on Monday learned that the pound had droppd. "Without even trying," says Gray, "John made a dollar a yard."

Coleman, who is prowling his party and overhears her, is only half-amused. "That's the only thing we saved money on this hotel," he grouses.

"He is a man who really wanted to be rich," says an old acquaintance. "He looked rich but wasn't." He was the son of a successful plumbing supply dealer in the affluent suburban Boston community of Chestnut Hill.

He went to Lawrence Academy in Groton, Mass. (the same town, if not alma mater, of Franklin Roosevelt and John Kennedy), got his degree in history from Rutgers, took night classes at Boston University and did a brief stint at Harvard Business School.

Two of his three marriages ended in divorce, and he is now separated from his third wife, Joanne Field Coleman, daughter of the late Chicago department store magnate Marshall Field.

Coleman's other wives also had successful parents. Linda Lichtenberg Kaplan, who lives in Washington, was the daughter of the attorney representing the firm that built Watergate. Coleman's second wife, and mother of his three children, is Margo Lederer Howard of Los Angeles, the daughter of columnist Ann Landers and Chicago businessman Jules Lederer.

The impression among his friends and colleagues is of a Boston Brahmin whose blood is blue, money old, social connections flawless and taste, consequently, refined. Chicagoeans, who like to point out that he isn't worth millions by accident, portrays him as a discriminating consumer, with homes at the Vineyard and in New Hampshire; apartments on Fifth Avenue and Lake Shore Drive; a preference for Tiffany gifts, Rolls-Royce Corniches, expensive clocks and correct (if dealer-selected) art.

"In a lot of ways," he is saying during an interview between bites of chicken hash, "Washington is probably the fastest-growing city in the world."

The chicken hash a la Jockey Club is an authorized version of the original served by New York's "21," an "old friend" which also manages Cricket's, the restaurant in his Chicago hotel named after a daughter.

"I don't know anything about the restaurant business," he says, sipping Perrier.

Apparently he did not know a whole lot more about the hotel business, because until he bought the Tremont and White Hall Hotels, he had just been making money - in investments and packaging of industrial and pharmaceutical products.

A midwesterner who remembers him as "not the most socially secure person in the world" but nobody's fool in business, calls him "quite an operator, big enough to do what he wants in Washington."

One acquaintance says Coleman's "finest hour" came in 1964 in Omaha where he wanted to build a $1 million townhouse complex.

"He noticed there were lot of handsoout" among city officials he approached for rezoning approval, says Hugh Fogerty, retired managing editor of The World Herald. "He became convinced it was a shakedown."

Before it was all over, Omaha's mayor had been indicted and thrown out of office (though he was later acquitted) and five people sent to prison.

Characteristically, Coleman pulls back from discussing it or anything else connected with his past. "There was a situation there," he says of his Omaha adventure, "and I wasn't going to fight the political situation the rest of my life."

"John enjoys the game of being in the right place at the right time," says Joan Braden, who met him through Warnecke, who met him a couple of years ago at the opening of Neiman-Marcus in Chicago.

True to his style in Chicago where he bought and transformed two old residential hotels on the near northside into posh, luxury-class hostelries, Coleman tried to buy the best of everything and everybody to help with The Fairfax. He brought in Warnecke to restyle the facade, lobby and public rooms; Ann Gray to give it a period identity; Baker Furniture Co. to produce its reproductions of 18th-century antiques and New York's "21" to manage The Jockey Club.

Small, continental-type hotels for travelers who demand personalized service was the coming thing, he had decided as a result of his Chicago experience. The idea of preservation fascinated him. In Chicago he underwrote most of the restoration of the Water Tower, one of the few remaining landmarks left over from the Fire.

There is an air of expectation as Coleman begins moving onto the Washington social front, curiosity about whether his private entertaining will match that of the town's ranking hotelman, Marshall Coyne. Chicagoans see Coleman giving small intimate dinners but doubt he is out to "stir up" a contest.

"He's mysterious," says Warnecke, without elaborating. Ann Gray says he will "develop his own sense of friends."

In Washington terms, Coleman's "sense" of friends may be rather finely developed already. He opened The Fairfax, for instance, sooner than he otherwise planned because of a promise made last winter to "an old friend". Significantly the friend, former Secretary of the Treasury William Simon, became the hotel's first overnight guest in September.

"Yeah, sure," Coleman says, making no effort to disguise his impatience; he's interested in politics but only peripherally. More engrossing is Washington's potential in attracting the domestic convention industry.

He's on record before the Senate Appropriations Subcommittee for the District as promising to add 120 rooms and banquet facilities to The Fairfax when and if a D.C. convention center is built. Last night he said he gave his architect the green light to start drawing up the plans.

He does not consider his hotels "typical" of convention hotels, says a colleague, but neither does he want to frighten off "potential diners or sleepers."

"He's going to set a tone in the class where his hotel belongs," a class that Coyne's Madison dominates and that caters to , among others, the moneyed ranks of corporate travelers and those doing business for foreign interests.

Not even Coleman would try to make his Washington entree all by himself. He has bought help: Hill and Knowlton to do his public relations, Patty Cavin and Associates to do the community relations. Socially, if he finds it necessary, he can turn to friends to tell him the Who from the who .

"I don't know that he is going to anyplace just to get people to come to his hotel," says Braden. "But if I thought he were making a desperate mistake, I'd say 'don't do that.' I'm not sure he would listen."

He's not to be found in "Who's Who" though there are directorships and memberships in charities, clubs, foundations and societies that range from the board of Menningers Clinic to the board of the Chicago White Sox.

"I'm not a professional joiner," he says, "just the things I'm interested in."