It was "Rocky" for computers at the Sheraton Park. A $5,000 chess-playing machine, with a program homemade by a young San Diego couple in their spare time, took on a $5-million heavyweight of the cybernetic world and brought it to its transistorized knees.

The program, named Sargon II, designed and played on the kind of microcomputer people are now buying for home use, did not win the ninth annual North American Open Computer Chess Championship-but it came close enough to scare the giants in the field.

It was not only upset in the three-day tournament which began Sunday. The world champion, Northwestern University's Chess 4.7, lost the North American title to an upstart named Belle (developed by Bell Laboratories) using new equipment designed especially for chess.

But the David-and-Goliath struggle of Sargon against opponent program Awit and its enormous computer was the chief focus for computer specialists and chess enthusiasts in the final hours.

Unlike human chess contest, the tournament was noisy. But nobody minded because the "players" weren't listening. Most of them were hundreds of miles away, computers in New Jersey, Minnesota, Ontario and Alberta, connected to terminals at the hotel by long telephone lines and typewriter keyboards-which also added to the noise.

Computer chess wizard David Ley, the tournament referee, moved around the big exhibit room giving running commentary on the games, using six large demonstration boards. The crowd of several hundred computer specialists and chess enthusiasts applauded some moves, laughed at the rather frequent blunders made by the machines, and kept up a continual chatter about the games.

But in the last round, all eyes turned to the seemingly mismatched confrontation between the $5,000 Sargon II and the $5 million Awit.

Those who watched the long, see saw battle had a spectacle worth their effort: one of the great, symbolic confrontations of brain against muscle since Muhammad Ali fought Joe Frazier. The chess was far from perfect (both sides made several mistakes), but that only added to the suspense: Would the computers, with their limited vision, see possibilities that were obvious to human players at the tournament?

Sargon, developed by the husband-and-wife programming team of Dan and Kathe Spracklen on their small home computer over the last 15 months, was not really competing for top honors in the tournament.

"Anyone can set it up on home equipment that costs about $1,100-a little slower than what we're using here." Kathe Spracklen said modestly. "We're publishing both our code and our program, because we think it would be nice if not everynone had to reinvent the wheel."

The Spracklens described their program's style of play as "more human" that that of most chess-playing computers and explained that, lacking the muscle of a big machine, they "had to program for brains."

"The big guys like Belle or Chess 4.7 could stomp over us and leave nothing but the footprints," Kathe Spracklen explained. "They can evaluate 8,000 positions per second. We can only do 40. Fortunately, in a four-game tournament, we didn't have to play them." But in terms of size, if not finesse, most of their opponents were still formidable. Awit certainly was. The program, designed by Tony Marsland, was connected by telephone line to a monster Amdahl 470 V/6 computer in Edmonton. Alberta-a machine that is spoken of in reverential tones by computer experts.

In the climactic game, Awit's programmer saw a forced checkmate against his brainchild, pointed it out to the Spracklens, and then breathed a sigh of relief when the computer missed it. "Now, I'll be happy with a draw." he said. Forty moves later, after several reversals of fortune, he was still hoping for a draw and the chances looked good.

"Now," said Levy's voice over the loudspeaker system, "the moment of truth," and the audience laughed. Sargon, with an overwhelming material lead, had immobilized Awit's pieces and faced the threat of stalemate.

Sargon's king had to move out of the way to give Awit's king a chance to move-and after that the victory would be routine. But would the tiny computer know enough to make a move that was not based on pure, blind greed?

The noisy room grew silent for almost a minute: then Sargon moved 62, K-B6, and the applause was overwhelming. Sargon won easily four moves later and tied for third place, immediately behind the giants, Belle and Chess 4.7.

"We never dreamed we would finish so high," said Kathe Spracklen. Sargon had been ranked ninth among the 12 participants going into the tournaments.

At the awards ceremony, after handing out the trophies, Levy said that. "The most remarkable performance was that of the microcomputers. I'm beginning to agree that perhaps when Bobby Fischer hands down his mantle, it will be to something you can put in a matchbox."

A note of rueful agreement was added by Edward Lacker, 93-year-old international master who has been conducting a running grudge match with Chess 4.7 and came to the tournament to play against it. When the awards ceremony began. Lasker had not finished his game, but he left it in a hopeless position to make his announcement:

"My contention that computers cannot play like a master, I retract. They play absolutely alarmingly. I know, because I have lost games to 4.7. The only deficiency is that they cannot always handle certain very subtle positions-which are not always well-handled by masters." CAPTION: Picture 1, Kathe and Dan Spracklen, by Joe Heiberger - The Washington Post; Picture 2, The ninth annual North American Open Computer Chess Championship by Joe Heiberger - The Washington Post; Illustration, The moment of truth: Sargon (white) to move.