Vitas Gerulaitis, the darling of Manhattan's East Sied disco set, has been disappointed to discover that he is not adored by the rank and file of tennis fans here in his hometown.

A street kid who grew up in Brooklyn and Queens and escalated socially into the jet set that hobnobs at Regine's and Studio 54, "Broadway Vitas" assumed he was the People's Choice of everybody in the Big Apple.

He was disillusioned and a little hurt when he learned that some people resent his flamboyant life style and flip wit. He has grown accustomed to the harsh sound of people cheering for his opponents at the new National Tennis Center in Flushing Meadow Park, which is practically in his backyard.

But Gerulaitis - seeded No. 4 behind Wimbledon champion Bjorn Borg, Jimmy Connors and defending champ Guillermo Vilas - finally got the full and vocal support of the crowd yesterday when he came within two points of being knocked out of U.S. Open, a championship he wants desperately to win. . . . and thinks he can.

The grandstand court, adjacent to the massive 19,500-seat Louis Armstrong Stadium where Vilas was siultaneously beating 1971 champion Stan Smith, was jammed to its 6,000-seat capacity for the final set of the 6-4, 3-6, 7.5 escape by Gerulaitis from the clutches of Andrew Pattison, a 29-year-old journeyman pro from Rhodesia who now lives outside Austin. Tex.

Gerulaitis twice was down a service break in the final set. Pattison served for the match at 5-4 and got to 30-15, two points from victory, before Gerulaitis summoned his last reserves and ran off seven straight points to reach safety. When it mattered, he brought to bear his quickness, nerve and a nice touch on two crucial offensive lobs.

The gallery screamed and applauded, but too late as far as Gerulaitis is concerned. For him, the love affair is over.

"I want to win for myself and a few close friends," he said. "The spectators paid their money and they can cheer for whoever they want. I don't care anymore."

Gerulaitis was one of several seeded player tested yesterday afternoon for the pleasure of 16,762 matinee customers on a brilliantly sunny late summer afternoon.

Vilas had a much tougher time with Simth on the hard rubberized asphalt courts here than he did on grass in the first round at Winbledon this year, but he answered the once-oppressive, 31-year-old Californian's serve-and-volley attack with aggression of his own.

The difference between them was only a few points, but Vilas made fewer errors when they counted. One break decided the final set. A couple of bussing topspin passing shots got Vilas to 0-40 on Smith's serve at 2-3. Smith served two of the break points, then netted an easy backhand first volley, the sort of careless lapse that has cost him so many matches in recent years.

Groans arose from the stadium crowd - which was noisily behind Smith, the All-American Eagle Scout who mysteriously lost the world-boating form that made him the top-ranking U.S. player in every year except 1970 between 1969 and "73.

Smith had one point to break back as Vilas served at 4-2. At 30-40, the Argentinian left-hander kicked in a good first serve, and Smith chipped a little backhand return across court that caught the net and fell back. Vilas dug in and held, and Smith never challenged when the champ served for the match two games later, closing out a 6-4, 3-6, 6-3 triumph.

Many thought the Stan Smith of old would have gone for a bolder return, hitting out to pressure his opponent, but he said he dinked his return because he was surprised by the bounce.

"It came up higher than I expected, so I wasn't able to put much power onto the return," he said. "It was a good serve, a kicker."

Smith, who had come into the Open as confident as he has been in some time after winning a tournament in Atlanta last week, thought he might have played too boldly.

"I think I could have been a little steadier on my ground strokes and not pressed him quite so much. Maybe I tried to get in too fast," he said.

Vilas disagreed.

"He was hitting very good approaches. He was risking a lot, but on the right points. I tried to overpower him, but he was all over the net," said the winner of the last U.S. Open on clay, at the West Side Tennis Club in Forest Hills Last year.

Smith's longtime doubles partner, Bob Lutz, ousted No. 13 seed Jose Clerc, who is a fast-improving Argentinian Davis Cup teammate of Vilas, 6-3, 6-2, but this was hardly an upset because Lutz grew up on cement courts in California.

He served and volleyed superbly yesterday, as he did in beating New Zealander Chris Lewis and fellow Californian Hank Pfiste in the first two rounds.

No. 5 seed Eddie Dibbs, winner of three tournaments this summer, saved five break points in the first game of the final set of his 7-6, 4-6, 6-3 victory over Balazs Taroczy of Hungary.

Dibbs was down, 0-40, but served four unreturnable serves to get out of the game. Taroczy had considerable trouble returning off the backhand, and Dibbs preyed on that side with the serve he has beefed up considerably with a remodeled toss that puts the ball higher and more out in front of him.

One other seeded player was beaten yesterday afternoon - No. 14 Wojtek Fibak, who fell to the thunderous serves of Butch Walts, 6-4, 7-5.

Gerulaitis lost his serve to trail Pattison, 2-3, but immediately broke back with a strong game that he sealed with a lob winner.

Pattison broke again for 5-4 on his fourth break point in a game that went to deuce six times. He was attacking Gerulaitis's serve, especially his short second delivery, starting eight feet behind the baseline but moving in and taking the ball as he barrelled in roward the net.

A forehand return winner off a second serve got him the break, but from 30-15 in the next game Gerulaitis cracked a backhand cross-court passing shot and lofted an offensive job that the powerful but less-than-nimble Pattison could not retrieve. At 30-40, Pattison was called for a foot fault. Then he drilled out a swinging forehand volley.

Greulaitis held serve at love and broke Pattison for the match. He got to match point with an nice running backhand down-the-line pass, and won when Pattison knocked a forehand across court into the next after Grulaitis got in behind another forcing lob.

"At 5-4, things looked pretty bleak. I was ready to cancel plans for my victory celebration," Gerulaitis said. "But I played aggressive games to break back in the third sets, and they finally called some, foot faults on him. He had been foot-faulting all the way through and camping on the net."