Dick Stockton sagged several times but refused to buckle today, and in the end produced perhaps the finest two sets of tennis he ever played to dethrone Jimmy Connors in the final of the $200,000 U.S. Pro Indoor championships.

Stockton's 3-6, 6-4, 3-6, 6-1, 6-2 triumph gave the soon-to-be-26-year-old Long Island native, now an adopted Texan, the biggest title of his four year pro career, $40,000 and the satisfaction of his first victory over Connors since 1969.

The match lasted a little more than three hours and was full of the undulations and subtle shifts in momentum and psychology that make tennis fascinating.

Stockton, a sturdy 6-foot-3, 180-pounder who is ranked No. 7 in the U.S., six places behind Connors, has a game that is colorless and straightforward but fundamentally sound.

He is always aggressive on his own serve, and has learned to wait out opportunities to attack his opponent's. Today he merged all the bits and pieces in those magnificient final two sets and ultimately defused the explosive power of Connors' all-court game.

"I think I hit the ball unbelievably well the whole match, and in the end I just put the shots together - two, three, four a game," said Stockton, who volleyed well throughout and served 11 aces, seven in the last two sets.

Stockton's style and grim, humorless court demeanor do not warm the heart. He looks like the bearer of bad news, and always seems either hermetically sealed in concentration or irritated during a match.

He steadfastly refused to join any of the humorous asides and by-play in which Connors engaged the first three sets, but eventually his victory was popular with the record crowd of 14,571 that brought warmth to the Spectrum, where the thermostat was again turned down to conserve fuel.

Stockton has won four World Championship Tennis (WCT) tournaments since turning pro after winning the NCAA singles title for Trinity (Tex.) University in 1972.

This was the most important to date financially, artistically, psychologically. The Philadelphia tournament is the heavyweight of the 12 events in the $2.4 million "World Series of tennis" that qualifies the top eight competitors for the prestigious WCT finals in Dallas in May.

Connors, the defending champion and No. 1 seed, was the final victim in a tournament in which the favorites were marked men. Seven of the top eight seeds were beaten before the quarterfinals, and finally Stockton (seeded No. 12) ousted Connors, who had won 26 straight matches in WCT events.

Stockton recalled yesterday that he first played Connors in the 1961 Orange Bowl Juniors. "I was 10, he was 9," he said. "I won that one and never lost to him until I was 22 years old."

As a junior player, Connors was a skinny kid who had not grown, physically, into the aggressive mold he knew was right for him. Stockton, who terrorized the juvenile set the way Connors now does the men's circuit, winning a record 20 national junior titles in eight years, held the uppper hand then, but had last beaten Connors in the semis of the 1969 national juniors. Since then, Connors was 6-0.

"There's a group of American players about my age who grew up with Jimmy and aren't awed by him," Stockton said today. "We know he's great; he can wipe us off the court some days. But we've beatn him in the past and feel we can do it again.

"Some foreigners are just awed by him. They go out there thinking they have no chance and lose, 6-2, 6-2. Some of us think he's No. 1 in the world but know that he can be beaten."

Stockton served well throughout, getting in two-thirds of his first serves (87 of 133). He didn't lose his serve after the fourth game of the third set, when he paid for missing five of six first deliveries.

Connors didn't jump on the second ball in Stockton's only shaky service game thereafter. It came at 3-1 in the fourth set and turned out to be the crux of the match. Stockton started with a footfault, missed seven of nine first serves but escaped from 0-40 and a total of four break points.

"I think it was the most important game," Stockton said later. "If he had broken back there (after Stockton had broken for a 2-0 lead), he might have gotten into a groove and run right over me."

Instead, Stockton pulled himself up by the sneaker straps and broke Connors' serve in the next game - on his fourth break point, after four deuces in a game that was filled with torrid, deep rallies.

From then on Stockton expanded, winning a total of seven games in a row to 4-0 in the fifth set. In the last five of those, he conceded only five points.

Flying high on a wellspring of confidence, Stockton got consistent pace and depth on both his first and second serves, and mixed them intelligent.

Connors' returns, which had been as ferocious for three sets as they were in his earlier matches (he won nine straight sets to get to the final), lost their sting and accuracy under the deluge.

On Connors' serve, Stockton stayed farther back, especially on the second balls that he had earlier tried to chip and follow to the net.

Stockton did most of the running in the rallies, as Connors moved him from side to side, but he did not wilt. He kept the ball down the middle, not giving Connors the angles he loves, preventing him blasting outright winners.

Toward the end of the third set and early in the fourth, Connors began missing on forehand approach shots, hitting either long or into the net. That is usually the first part of his game to go, and later he began making unforced errors off both wings. He was getting beaten from the back-court, and had no chance to charge in for the slashing volleys he was hitting earlier.

"I watched the news on TV last night, and the sportscaster built up this match by saying I had absolutely no chance," Stockton told the crowd at the presentations, before Bob Hewitt and Frew McMillan came out and won the $14,000 top prize in doubles over Wojtek Fibak and Ton Okker, 6-1, 1-6, 6-3.

"The anchor man as an old friend of mine from school, Michael Tuck, and he was standing up for me. I think Mike Tuck, my wife, and I were the only people in the world who thought I could win."