US Open. For players, the allure is some $3.4 million in prize money and a `Grand Slam' title. For fans, it's the tennis -- 23 sessions ending this Sunday that showcase the superstars of the game.

ONE can fairly argue that a fuzzy yellow tennis ball should momentarily replace a shiny red apple as the symbol of New York City. Ten days ago the United States Open tennis championships began their traditional two-week run in the Borough of Queens. By the time the final shot is hit Sunday night, the tournament is expected to set a attendance record, with well over 400,000 spectators.

It is the mega-event of American tennis, the richest in the world, with $3,450,800 in prize money. It ranks along with Wimbledon and the French and Australian Opens as one of the four international ``Grand Slam'' championships -- and the only one played in a public facility.

It is also quintessentially New York -- big, bustling, and intense, with plenty of corporate trappings -- sort of a Times Square teeming with tennis energy.

The city environment is certainly reflected in the surroundings. The National Tennis Center, the 16-acre home of the Open, sits in the midst of Corona Park, a sprawling playground once the site of the 1939-40 and 1964-65 World's Fairs and now a regular gathering place for a rich ethnic mix. Nearby, planes roar into flight at La Guardia Airport, subway cars clatter along elevated tracks, and baseball fans funnel into Shea Stadium. The majestic Manhattan skyline is not too far away, either, and can be viewed from the top row of center-court seats from a distance of some 10 miles or so.

Ticket holders in these seats peer down from the rim of the world's largest permanent tennis amphitheater, the 20,000-seat Louis Armstrong Stadium.

This is where the game's superstars are showcased and the major matches played. But the action here only scratches the surface. At times, especially early in the tournament, the numerous outlying courts provide a wonderful smorgasbord of matches.

They are played either in the 6,700-seat grandstand or at any of more than a dozen field courts, where the metal bleachers sometimes overflow with fans. Many hunt out the name players or an exciting match. News of the latter can spread quickly by word of mouth or via the Scoreboard Plaza inside the main gate. This post provides information on matches in progress, including big-screen video coverage of some. An `American' surface

In separate 128-player draws, men and women vie for the major singles crowns and $210,000 each in first-place prize money. The Open, however, is really many events rolled into one. There are junior titles, senior titles, doubles galore, and even a ``Family Challenge'' playoff. The stars of tomorrow are on display, as are many past greats, such as Billie Jean King, Stan Smith, and John Newcombe, whose matches are often wonderful fun.

The grounds are trimmed in red, white, and blue, but the player entry list reads like a Rand McNally index: India, Israel, Peru, Greece, New Zealand, Nigeria, the Soviet Union, and seemingly all points between.

Last year two Czechs, Ivan Lendl and Hana Mandlikova, made off with the grand prizes, this even though the medium-fast, rubberized asphalt on which the open is played has been called an ``American'' surface and presumably favors native sons and daughters accustomed to composition courts.

For years, beginning with the birth of the US championships in 1881, play was on grass, mostly at the West Side Tennis Club in nearby Forest Hills, N.Y. The club's manicured lawns were still underfoot in 1968 when young amateur Arthur Ashe won the first actual ``Open,'' ending the lockout of professional players.

The tournament tried clay courts for several years in the 1970s but gave up on the idea in 1978, when the US Tennis Association (USTA) moved the tournament out of Forest Hills to the hard courts of the new, more spacious National Tennis Center.

Only five miles separate the sites, but the switch was a major leap from a gracious club atmosphere to sort of a gleaming big-league facility better suited to the masses.

Slew Hester, an oilman and former president of the USTA, is the visionary in this case. He spied the present location from an airplane and made a deal with the New York City parks department to build and operate the National Tennis Center on city property. The center is used by the public 10 months of the year, with the USTA maintaining exclusive rights to it for 60 days. Festive air prevails

Last year the Open generated $9 million in revenue, or nearly three-quarters of the operating income the USTA uses to organize its programs, many at the grass-roots level.

These are the sorts of programs that keep the sport growing, which is why Hester feels no qualms about leaving behind the tradition associated with Forest Hills. ``If they want tradition, we'll plant some ivy,'' he says.

Ivy is only part of the modern package. Potted flowers, wide walkways, shade trees, a pricey merchandise arcade, sponsor party tents, and an international food village lend a festive air to the complex.

The real allure, though, is the world-class tennis, a veritable feast's worth -- 23 sessions, including night matches that sometimes run past midnight.

But, hey, why not? After all, this is New York, ``the city that never sleeps.''