Before Bjorn Borg steps onto Wimbledon's center court to play his first match Monday, he will pray for partly cloudy skies.

London is at 61.3 degrees north latitude, so when Borg serves from the north side of the court, the sunlight will be directly in his eyes. His first-round opponent, Peter Rennart, also is right-handed and, too, will battle the sun.

In addition to Wimbledon being the world's most prestigious tennis event, it is also the most northern of the major outdoor events. (Only a $75,000 event in Bastad, Sweden, is farther north.) As a result, some matches won't finish until 9:15 p.m. It doesn't get dark until about 10:45 p.m. The first day of the Wimbledon fortnight is also the second longest day of the year.

Because of prospects of having to play at such a late hour, many of the world's best players skip doubles and the mixed doubles. Borg, for example, hasn't played doubles since 1974.

There are many young players here participating in their first grass-court event. There is always a strong contingent of American collegians, such as Tim Mayotte, NCAA champion. Most arrive via the qualifying event played at the Roehampton Club, about four miles from Wimbledon.

Since most are amateurs, few are ranked in the top 300. Yet they all hope to emulate John McEnroe's feat of 1978, when he won three qualifying matches and played his way to the semifinals before losing to Jimmy Connors in four sets.

Matches here are played on grass, and that is almost an anachronism. On the Volvo Grand Prix circuit, only Australia and New Zealand have grass-court events. The typical blade of grass is about 1 1/2 inches long or about an inch longer than those sheafs found on a fast golf green. And each is clipped at an angle of roughly 45 degrees.

The groundskeepers reckon that there will be less bruising and fewer "split ends" if the daily snippings are not done at right angles to the blades. "No further attempt is made to allow the lawn to grow a bit longer either the base line or the T-junction where the service and center-service lines cross. At the courts wear over this two-week event, these two areas will turn brown faster than the rest of the courts.

But the courts get a break. There is no play on Sunday and if it's warm, sunny day the grass will grow about an eighth of an inch in 24 hours. And since the second Monday is traditionally the ladies' quarterfinals, their two-put-of-three-set matches do far less harm to the grass than a long five-set men's match.