A year ago, when the new home of the U.S. Open tennis championship was little more than an architect's rendering, U.S. Tennis Association President W. E. (Slew) Hester vowed that 16 acres of neglected and decaying city-owned parkland on the site of the 1939 and 1964 World's Fair could be developed into the world's largest spectator tennis complex in 12 months.

Having cut through the red tape of the notorious bureaucracy and negotiated a 15-year lease agreement with the New York City Department of Parks and Recreation in less than four months, Hester was confident he could overcome the union disputes, cost overrun and construction delays that are an inescapable part of building dreams in the Big Apple.

Doubters far outnumbered believers. But Hester - a 66-year-old wildcat oil man from Jackson, Miss., who looks and sounds like a cigar-chomping southern sheriff but has proved to be a dynamic leader - was determined to move the Open this year from the stuffy and congested West Side Tennis Club in nearby Forest Hills.

To those who asked what the spacious new facility in Flushing Meadow Park would be called, he replied with a wink: "If it's done on time it will be the USTA National Tennis Center. If not, they'll call it the 'Slew Hester Memorial.'"

The USTA National Tennis Center it is, and Hester is alive to see what many considered his wide-eyed folly open on scheduled.

The impressive complex, complete with 27 hard surface courts and twin stadiums seating 25,000 spectators, will be dedicated tonight with ceremonies inaugurating the 98th U.S. championships, the 11th of the Open era and the richest ever, with $507,000 in prize purses.

No. 1 seed Bjorn Borg, the French and Wimbledon champion who is seeking his first U.S. Open title, and the third leg a possible Grand Slam, will play the first match on the green, medium-fast center court of the 19,582-seat Louis Armstrong stadium against 38-year-old Bob Hewitt.

California prodigy Tracy Austin - who a year ago, at age 14, reached the quarterfinals as the youngest player to compete in the U.S. championships - then opens the women's singles against Trish Bostrom, 26, of Seattle.

Bostrom is a late refugee from the qualifying competition, a replacement for veterans Francoise Durr, who was drawn against Austin but ironically, had to withdraw after falling from a bicycle over the weekend.

Originally the defending champion, Guillermo Vilas (seeded No. 3 this year behind Borg and Jimmy Connors) and Chris Evert (No. 2 behind Martina Navratilova, her conqueror in the Wimbledon final) - were to have the honor of playing the first matches.

But Evert, striving to become the first woman to win four straight U.S. singles titles since Helen Jacobs in 1932-35, drew a first-round bye and Vilas, who as struggled this year, was granted a one-day respite for health reasons.

The26-year-old left-hander, unable to find the form that won him the last U.S Open at Forest Hills in the midst of a splendid 50-match winning streak last year, was hospitalized Saturday for treatment of a stomach ailment and tendinitis in his left shoulder.

The opening festivities, beginning with a performance by the Olympia Brass Band of New Orleans, are expected to attract a number of dignitaries and celebrities. Among the participants will be New York mayor Edward Koch and Louie Armstrong's widow, Lucille.

The stadium, built as the Singer Bowl for the 1964 World Fair, was rechristened as a memorial to jazz great Armstrong, who lived in the nearby Corona section of the borough of Queens. The musician's name has been retained now that the structure has been rebuilt and enlarged into the most significant new international tennis arena since the modern all-England Club at Wimbledon, in suburban London, and State Roland Garros in Paris were constructed in the 1920s.

The center court is a massive, modernistic edifice built in four steeply banked tiers: eight rows of courtside boxes, 20 rows of blue-backed aluminium seats, 12 rows of gray bleachers, then 16 rows of blood red bleachers.

There are no granite eagles perched as sentries atop the stadium, as there were at Forest Hills (home of the U.S. championships from 1923 until last year but the top row of seats affords an eagle's eye view of the gladiators-with-rackets 90 feet below. Spectators at this height might fear nose bleeds, but they get a magnificent view of the distant New York skyline and the silver "Unisphere" and other World's Fair monuments that decorate "the Meadow."

The stadium is hardly intimate - the recent surge in tennis popularity has done away with clubby settings in which every spectator was close enough to feel a part of the action - but there does no appear to be a bad seat in the house.

The adjacent granstand - separated from its Siamese twin by a two-story "core building" housing locker rooms lounges, restaurants, offices and the like - is a 6,000-seat horseshoe of blue and red bleachers around the second "show" court. Behind it is a Long Island Railroad station and an elevated walkway to a subway station and the 8,000 car parking lot which the new complex shares with Shea Stadium.

The 25 outside courts - all lighted and many with 600-seat banks of scaped mall with the most striking of the World's Fair structures as a back-drop.

They have been grouped so as to permit preservation of the stateliest trees - oaks, maples, plus "The Grove," a crescent of 40-year old sycamores that has been turned into one of several pleasant picnic spots on the picturesque site.

The landscaping is far from complete. Furrowed plots and giant mounds of earth, turned to mud by heavy showers yesterday morning, surround some of the yellow-and white-striped entertainment tents because sod has not been fitted into place.

The litter of excellerated construction - sawdust, unixed cement, pieces of pipe and cable, spare girders and planks, discarded spools and drums - clutter parts of the grounds. Payloaders, forklifts, and other heavy equipment were busily and noisily at work well into the evening.

A rim of skyboxes and a retractable canopy over most of the stadium seats have been delayed until next year. An 11-court indoor tennis center, where the qualifying rounds were completed yesterday, is unfinished. Still, it is something of a miracle that the USTA National Tennis Center, which will be open to the public the rest of the year is functional enough to host the Open.

A hardhat force of 340 men including 160 electricians has been working around the clock in recent weeks, when construction began in earnest last spring, the budget was $6.5 million. With overtime pay, cost of construction has climbed to more than $10 million.

Yesterday Hester sat in the stadium observing the last full day of building and sprucing. Welders reinforced girders, carpenters hammered railings, and painters almost ran up their backs, splashing a fresh blue coat on wood and nails still hot from pounding.

Technicians adjusted scoreboards and sound systems installed only last week; other workers attended to cosmetic problems - nailing signs into white chrysanthemums to their places at court side.

"No eleventh-hour traumas. If you've got the faith, you can make it. We had faith," said Hester, who seemed the calmest man in the place."Only our enemies" - presumably, he was referring to the embittered West Side Tennis Club board that tried to block the move from Forest Hills - "thought we'd fail.

"We have spent a lot of money on overtime. Nobody knows exactly how much yet. Everyone was told, 'Work night and day, get the job done, and send the bill.' We couldn't affort to do anything else because we didn't have any other place to play."

The only work stoppage came last Wednesday when Connors - one of many players who have been working out here for several days, getting the feel of the quicker than expected, cushioned hard courts - tried out the center court. "We had him hit on all the courts, but when we put him in the stadium, the workmen sat down and watched. We couldn't have that," said Hester.

"I found that the best way to get things built fast is to be always available, always optimistic, and to always say yes - except when Jimmy wants to practice in the stadium," grinned Hester, citing his formula for miracles. "I'll worry about the cost next week. May be the USTA will want a new president then."