Moments after the schedule for the opening day of play at Wimbledon had been posted Saturday, a group of players crowded around the door of the referee's office to check on their matches. Boris Becker stood outside the circle. "I think," he said, smiling, "I know when I'm playing."

As defending men's singles champion, Becker will play Monday afternoon. Tuesday afternoon, Martina Navratilova, the four-time defending women's champion, will play. Beyond that, the 100th version of "The Championships" -- Wimbledon to everyone but the English -- is full of question marks.

"This is the year that there's no one player that you look at and say, 'He's going to be very tough to beat,' " said Tim Mayotte, one of a dozen men given a chance to win. "I think I can win, so do a lot of other guys."

Among the women, most observers expect the usual script: Navratilova beating Chris Evert Lloyd in the final. That has been the scenario three of the last four years. Navratilova is seeking her seventh championship, Evert her fourth.

Steffi Graf, the latest challenger to their dynasty, is not here because of a severe virus. That leaves the usual players left to challenge: Hana Mandlikova, Pam Shriver, Helena Sukova, Claudia Kohde-Kilsch (who is hurt), Kathy Rinaldi and Zina Garrison.

The situation among the men could not be more different. Everyone, it seems, is a dark horse.

Becker is the defender, but many question if that role will be too much for him to handle at age 18. Ivan Lendl clearly is the best player in the world right now with a match record of 73-3 since August, but he becomes fidgety, uptight and nervous when he looks at the lawns of the All England Club. He even skipped the tournament one year, saying he was allergic to grass. Mats Wilander, the No. 2 seed, has played as if he is allergic to Wimbledon over the years. He has proven he can play on grass -- winning the Australian Open twice -- but has bombed out here annually, never getting past the round of 16. Last year, as the French champion, he went out in the first round to Slobodan Zivojinovic.

"I feel a lot better here this year," Wilander said today. "I have a very tough first round Scott Davis of the United States , but if I win that match I think I can do very well here."

Jimmy Connors feels the same way. If his body holds up, third-seeded Connors is capable of winning, even if he is two months shy of 34. He played very well at the Queens Club tournament in reaching the final before a groin pull forced him to default to Mayotte. He played two sets against Becker here Friday and pronounced himself fit. Whether he can stay that way for two weeks is the question.

There are others: Stefan Edberg won the Australian last year, is the best grass court player among the Swedes and feels comfortable here, having bought a flat in London recently. But does he have the fire to win Wimbledon? Henri Leconte, the dashing Frenchman who beat Lendl here last year, has all the shots but lost to Vijay Amritraj on Saturday.

"He hits no-brainers," Bud Schultz said after winning three games from Leconte then losing in their semifinal match Friday. "If they go in, you can't beat him. If they don't . . . " They didn't Saturday, and Leconte lost to Amritraj, a 32-year-old perhaps best known recently for a bit part on a TV series called "The Last Precinct."

There also are: Mayotte, the Queens winner who plays well on grass courts and has been to the semifinals here; Paul Annacone, who is likely to play Edberg in the second round; and Kevin Curren, the losing finalist a year ago who has played poorly of late but has proven he can serve anyone into submission.

For most of the players, this has been as easy a week of preparation as they've had here in years. The weather has been superb, one sun-drenched day after another. That is in marked contrast to the constant rain of last year's tournament.

Practices have been held in virtual privacy. Wimbledon looks more like a prison camp than a tennis grounds. Every gate is heavily guarded and almost no one was allowed on the grounds before Saturday.

Because of the tension after the U.S. bombing of Libya in April and the recent conviction of an IRA terrorist for killing five people in an attempt to assassinate Prime Minister Margaret Thatcher, Wimbledon officials are concerned about security. As a result, very few cars will be allowed on the grounds. Only seeded players will be driven inside the gates and everyone will have their bags checked before entering.

Opening day always is full of tradition and Becker's first appearance on Centre Court, even against Eduardo Bengoechea, should be dramatic. As the No. 4 seed, Becker is the lowest seeded defending champion since Jan Kodes was No. 6 in 1974 and the first defender not seeded first since Bjorn Borg was seeded behind Connors in 1977.

There are other Monday matches of interest: Wilander vs. Davis; Connors vs. Robert Seguso; Lendl vs. Leonard Lavalle; Mayotte vs. Alexander Zverev of the Soviet Union; and John Lloyd, playing perhaps his last Wimbledon, against South African Christo Steyn. In all, there will be 48 men's matches Monday and 16 women's matches.

Tuesday, the most intriguing match will pair Guillermo Vilas, the 15th seed, against Pat Cash. A semifinalist here in 1984, Cash has been out most of the last nine months. He had back surgery in the fall and had his appendix removed just three weeks ago.

"If I can serve, I can beat Vilas. I know that," said Cash, once ranked as high as No. 8 in the world but now ranked No. 418. "I just don't know if I have enough time. My stomach muscles still feel tight when I serve."

Cash wonders about his serve. Becker wonders about the inflammation in his right palm that has been bothering him. Lendl wonders about grass. And the rest of the tennis world wonders what will happen when Becker opens the tournament Monday afternoon.