The U.S. Open, played at the raucous U.S. Tennis Center in Flushing Meadow, begins Tuesday with sufficient subplots and mini-dramas to last the full 13 days.

On the surface, the main characters are John McEnroe and Chris Evert Lloyd, the defending champions who are top-seeded based on their victories in July at Wimbledon.

But the plot line that is the most intriguing and receives the most attention -- just like last year and the year before -- is Bjorn Borg's continuing quest to capture the one prize that has eluded him in his astonishing career.

Borg has played in the Open nine times and never won. He reached the final three times, in 1976, 1978 and 1980, only to be frustrated.

To add to his frustration, he has come to the Open three times with hopes of achieving the third of the four championships needed for the Grand Slam (French Open, Wimbledon, U.S. Open and Australian Open). Three times he has failed.

It is not as though his downfall is the result of a tragic flaw. Each year, there is a different reason for Borg's demise. In 1977 he defaulted to Dick Stockton because of a shoulder injury. In 1978 he was destroyed by Connors in the final after suffering a blister on his thumb. In '79, Tanner beat him in the quarterfinals and Borg and his coach, Lennart Bergelin, complained about playing at night. Last year he dropped two sets to McEnroe, came back to force a fifth set, then served horrendously to lose.

Of the Open, Borg says: "I don't think there is any jinx. I have tried very hard to win. For as long as I play tennis, my main goal will be to win it."

Borg is 25 and not having won the Open at that age is hardly a disgrace. But when you have won the French Open six times and Wimbledon five times, it is different. You are expected to win. Many now wonder if the seemingly implacable Borg is psyched out by the prize-fight atmosphere that reigns in Louis Armstrong Stadium during a big match.

By contrast, McEnroe and Connors thrive on the less-than-decorous atmosphere in the stands. Connors has won this title three times and pushed McEnroe to the limit in last year's semifinal, losing in a fifth-set tie breaker after more than four hours of superb tennis.

Connors will turn 29 next week and, not having won a major title since the '78 Open, is generally considered past the stage where he can win a major tournament.

McEnroe, going for his third straight title here, must be considered the favorite. He is coming off a decent summer, including a victory in the ATP Tournament last week. By contrast, Borg has not played a competitive match since losing to McEnroe in the Wimbledon final July 4.

Two men outside of the Big Three have legitimate chances to win this tournament: Czechoslovakia's Ivan Lendl and Argentina's Jose-Luis Clerc. Both are more comfortable on clay, but can play on the faster asphalt of the tennis center.

Lendl proved that in July when he beat an admittedly tired McEnroe in the Davis Cup opener played on the center court. He has beaten McEnroe the last three times they have played. But he would have to play Borg in the semifinals if the seedings held up and that would be a difficult match for him on the faster surface.

Clerc, the fifth seed, was the hottest player in the world this summer. He won four tournaments in a row on clay, beating Lendl twice during that span. At 23, he is emerging as a genuine star, having unseated Guillermo Vilas as the No. 1 player in Argentina.

The other men's seeds are players going in various directions on the ladder. Vilas, the 1977 champion, has dropped to sixth in the seedings and Gene Mayer, as high as fourth in the world in the last year, is now seventh. Mayer has never played well in a major tournament and defaulted midway through his first-round match last year.

Eliot Teltscher, 22, a young player on the rise, is the eighth seed, followed by Tanner, Brian Teacher, Peter McNamara, Johan Kriek, Yannick Noah, Wojtek Fibak, Vitas Gerulaitis and Brian Gottfried. None of them can be expected to get past the semifinals.

The women's draw is no more wide open than the men's. Evert, the five-time champion, must be the favorite although third-seeded Tracy Austin beat her, 6-1, 6-1, in the Canadian Open final last week, only Evert's second loss this year.

Evert and Austin have reversed roles this year. One year ago, Austin was the No. 1 player in the world, the defending champion and a player who had beaten Evert three times in 11 days early in the year. Evert, coming back from a brief retirement, had to prove herself once again.

She did. In a stirring semifinal, Evert came back after losing the first set to dominate Austin, 6-1, 6-1, in the last two sets in a match Evert admitted she wanted more than any she had ever played. She then beat Hana Mandlikova for the championship.

Outside of Evert and Austin, the only women who seem capable of winning are Mandlikova, who beat Evert on her way to winning the French Open this year and then lost the Wimbledon final to her; 16-year-old Andrea Jaeger, who is the No. 2 seed, and Martina Navratilova, who is trying to regain dominance. Navratilova is seeded fourth, just ahead of Mandlikova.

The other women's seeds, in order, are Sylvia Hanika, Wendy Turnbull, Pam Shriver, Virginia Ruzici, Mima Jausovec, Barbara Potter, Bettina Bunge, Regina Marsikova, Kathy Jordan, Sue Barker and Dianne Fromholtz.

Early upsets and controversy will thicken the plot further. They are inevitable in the high-charged New York atmosphere that makes players, even those with nerves of steel, such as Borg, jumpy.