Sixteen-year-old Tracy Austin ended Chris Evert's four-year monopoly to become the youngest U.S. women's singles champion in history, and John McEnroe routed his Long Island Neighbor, Vitas Gerulaitis, to become the youngest men's champion since Pancho Gonzalez in 1948 at the U.S. Open tennis championships today.

A record crowd of 18,288, which brought the total paid attendance for the 13-day tournament to 305,311, watched California Austin torpedo the seemingly unsinkable Evert, 6-4, 6-3. Details on Page D1.

Austin, who won't turn 17 until Dec. 12, supplanted the late Maureen Connolly (1951-52-53) in the record books as the youngest singles champion with ground strokes so hard, accurate and tenacious that comparisons to Connolly and Evert were inevitable. Evert, who had won 35 matches in a row in the Open, was foiled at the last hurdle in her quest for an unprecedented fifth consecutive singles title.

McEnroe, who celebrated his 20th birthday in February, completed the triumph of youth, serving and volleying masterfully and intimidating even the fleet Gerulaitis with his quickness and razor-sharp strokes to win, 7-5, 6-3, 6-3, later in the evening.

This last day of the Open began in the golden glow of an idyllic late summer morning.

It began under the big, carnival-style, yellow-and-white-striped tents used for corporate entertaining and public picnicking at the National Tennis Center in Flushing Meadow Park. The area once was a desolate dump, as readers of "The Great Gatsby" will remember, but now it is a pleasant and picturesque refuge in the bustling borough of Queens.

The gates of the 16-acre public complex, where the U.S. Open moved last year from its home of 54 years, the private and stuffy West Side Tennis Club in nearby Forest Hills, were opened to the public at noon today, two hours before the start of the mixed doubles final.

If Wimbledon, played at the stately All England Lawn Tennis & Croquet Club in suburban London, is the cathedral of tennis, then the U.S. Open is its Big Top, its Ringling Brothers, Barnum & Bailey.

In comparison to Wimbledon's church-like decorum, the Open is a circus -- splashy, noisy, occasionally outrageous and unblushingly commercial.

Merchants of tennis are everywhere, from the moment one steps off the subway and is besieged by hawkers engaged in a great T-shirt price war until the last departing spectator leaves "The Great Hall" -- an arcade underneath the stadium where one can buy anything from a shrimp cocktail to a can of Pierre Cardin designer tennis balls. (Why not?Would

you want to put a humble Spalding in the pocket of your Oleg Cassini designer tennis sports?)

The atmosphere of the Open has borrowed as much from football or baseball games at nearby Shea Stadium as from the long white flannel tradition of old Forest Hills.

When the wind blows from the southeast, jets roar overhead from LaGuardia Airport, just a mile away down Grand Central Parkway. Spectators move around during play and scream loudly for their favorites. New York ushers -- brusque, boisterous and eminently corruptible -- add to rather than alleviate commotion.

The National Tennis Center, with 27 outdoor and nine indoor courts, was built on city-owned land by the U.S. Tennis Association (USTA) at a cost of $12 million. It is open year-round to the public. It is in a public park. That is the beauty of it.

The land on which it was constructed has a storied past. In the 1920s, it was a dump -- the site of George Wilson's gas station and the famed oculist's billboard (the eyes seemed to be looking straight at you, no matter the angle) in "The Great Gatsby."

Fitzgerald referred to it as a "valley of ashes, where ashes grow like wheat." It was cleared eventually by Brooklyn politician Fishhooks McCarthy, who just happened to own a trash-removal business, and was scenically landscaped as the site of the 1939 and 1964 World's Fairs.

The structure that is now Louis Armstrong Stadium, centerpiece of the tennis complex, was built as the Singer Bowl for the '64 World's Fair. It was named for the jazz great who lived nearby when used chiefly for concerts by the city.

It was terribly rundown, in fact closed to the public, when W. E. (Slew) Hester, the wildcat Mississippi oilman who was president of the USTA in 1977-78, saw it from an airplane while landing at LaGuardia one day, and approached New York City officials about making the site available for a tennis center.

Through Hester's sheer persistence, energy and savvy in cutting through bureaucratic red tape, the complex was built in a year. The stadium was expanded and refurbished into a steeply-banked center court, in red, white and blue motif, seating 19,000 spectators.

Hester -- who planted a pot of ivy last year, marked with a sign reading "Watch Tradition Grow" -- talks of eventually making Flushing Meadow Park "more beautiful than Wimbledon."

That is unrealistic. Wimbledon has the charm of a sort of architecture that is passe. Its Center Court is a vine-covered, Elizabethan-style theater. Its grounds are spotlessly spruced, lined with shrubs and flowers. The site of the Open is a modern concrete stadium, with garish advertisements at courtside and plastic geraniums to add a splash of color to the green, asphalt-based hard court.

The surrounding parkland is attractive. From the top rim of the stadium, one can look out at the 1964 "Unisphere" and its surrounding fountains in one direction, the Manhattan skyline silhouetted like a distant magic kingdom in the other. But the tennis complex will always look more like a park than a manicured club such as Wimbledon. So it should be.

After all, this is the U.S. Open .

The tented pavillions -- some rented by corporate America for elaborate functions, others open to anyone who wants a leisurely meal or snack, from fresh fruit salad to chocolate mousse cake -- give it a Big Top appearance.

At times the Open smells almost like the circus, even without peanuts and elephants. It has a curious mixture of tantalizing and distasteful aromas: hamburgers cooking on charcoal grills; pungent knockwurst and sauerkraut; unemptied garbage cans astinking; disinfectant left behind by undermanned cleaning crews unable to cope with New York's grime rate.

Worst of all, there is an indescribable, mysterious stench in the grandstand that David Kenneth Specter, architect of the center, suspects is emanating from a drain where concentrated soft drink syrup was poured and, instead of disappearing, turned to decomposing sludge.

The USTA, which operates the tennis center under a 15-year lease agreement with the city, has promised to redouble its maintenance efforts next year.