The San Antonio Spurs defeated the Washington Bullets, 104-97, tonight at HemisFair Arena, but not before the visitors almost had pulled off one of the most incredible and improbable comebacks in NBA history.

Trailing by 34 points, 85-51, with 3:49 to play in the third quarter, the Bullets cut the margin to three points before succumbing. The comeback was led by Washington's angular 7-foot-7 rookie center, Manute Bol.

On the court for virtually the final 19 minutes of the game, Bol, often guarding Mike Mitchell, San Antonio's all-star small forward, blocked seven shots. Five of those blocks came in the final quarter as he spearheaded a defensive stand that limited the home team to 14 points in the period.

Bol's seven blocked shots in the half tied Elvin Hayes and Charles Jones for the Bullets' record.

"I believe that anything can happen in pro basketball," said Washington Coach Gene Shue, who must discover a way to win on the road. The Bullets have lost their last six games away from Capital Centre, where they face the Detroit Pistons Saturday night. "There isn't any lead that's safe. That's how I feel, because I've seen the damnedest things occur."

There were any number of extraordinary events here tonight. Gus Williams, scoreless in the first half, finished with 23 points, just two fewer than Jeff Ruland.

The game marked the season debut of Bullets guard Frank Johnson, who has been on the injured list recovering from a broken foot. To make room on the roster, Washington waived rookie guard Perry Moss.

Johnson, zero for five in the first half, helped begin the comeback with eight second-half points.

That drive was halted only by two great plays on the part of the Spurs. The first came shortly after a basket by Williams had made the score 97-90 with 2:55 to play. Trapping at midcourt, Williams and Cliff Robinson knocked the ball loose from Johnny Moore, who had a team-high 25 points, eight assists and seven rebounds.

Robinson threw the ball to Williams, who seemed to be cruising in for a layup. But out of the blue came Alvin Robertson to block the shot. The play led to two free throws by Artis Gilmore but it wasn't enough to finish off the Bullets.

That didn't happen until just 41 seconds remained in the game. Working against a rapidly dwindling shot clock, Moore beat the buzzer with a falling, twisting layup to make the score 101-96.

Of course, the most amazing aspect of the game was Washington's comeback. Or perhaps it was the way the Spurs controlled the game at the outset.

"They came out so hard," said Shue. "It wasn't that we weren't ready, they just swept us away. It took us completely by surprise. They just dominated play. Everything they did was right."

Moore scored 14 points in the first quarter as the Spurs took a 35-15 advantage. By the 7:27 mark of the second period the score was 47-20 and Shue was heard asking his team if there was a leader to be found in the bunch.

But the call for a few good men would go unheeded for the rest of the half (Washington trailed, 59-37, at intermission) and the great majority of the third quarter as well. The Bullets were losing, 72-43, when Shue sent Bol into the game, a move that seemed more out of desperation than anything else.

"We were just grasping at straws," the coach admitted. "But then, we finally hit a group and things started happening on the floor."

Many of those happenings were generated by the Bullets' trapping defense, a facet of the team that was very much in evidence during the exhibition season but hadn't brought much success since.

Despite the steals the defense generated, Johnson felt an even greater effect was that "it made us become more active, everyone started moving.

"Up to that time we were out of sync, just slow. But when we started pressing, it took them out of the flow. Suddenly they weren't getting layups. We had a funnel and we took advantage of it."

The eye of the maelstrom was Bol. One blocked shot led to a layup by Dudley Bradley. A short time later Bol stole a pass and began a fast break that ended with Williams' layup. Shortly after that Bol's rebound and outlet pass begat Williams' three-point field goal.

"I don't quit because I knew we could come back," Bol said. "That's why we play hard the whole time. I like playing hard every time and helping the team."

There was no question about his value tonight, part of which included bringing many of the 7,742 fans at the game onto the Bullets' side in the late going.

"I'll tell you what, Manute is going to have an effect in this league. Fans from all over the country are behind him," said a relieved San Antonio Coach Cotton Fitzsimmons. "We lost our jump shot in the fourth quarter and we wouldn't take the ball to the basket.