Top professional squash players from all over the country will converge here Dec. 5-7 for the $10,000 Washington, D.C., Open, part of the World Professional Squash Association tour.

The what tour . . . Squash? You got it. It's the latest thing to hit Washington since Calvin Lkein jeans and Perrier water.

More than 2,000 people are playing the high-speed game at The Washington Squash Racquets Club, the site of the tournament and a chic place to sweat and strain.Actually, the club looks more like the set of a Woody Allen movie than a place to burn off 600 calories an hour.

Even though 70 percent of the members had never played squash before joining the coed club, which opened in February, managing professional Tom Lane says it's the game of the moment.

"The image of the game has now changed. Notice I don't say (it's) changing.' The fact is, everyone can play now."

For years, squash had a reputation as a snob sport. "That's because most people learned to play the game in prep school, and then the only place to play after that was at an ultraexclusive private club," Lane says.

The game still is played at places such as the University Club on 16th between L and M streets NW. But as squash became more popular during the last decade clubs opened and made memberships available to men and women at moderate prices.

Although squash has had an upper-class image, it was invented in an English prison in the middle of the last century. The inmates at the Harrow Gaol decided that since they couldn't get beyond the walls, they might as well use them to keep fit. The game was called 'squash' because the inmates played with a very soft ball. (The hard, hollow ball now used travels at speed up to 150 mph.)

In the 1850s, squash became part of the curriculum at the prestigious Harrow School, a boys' prep school, and officials there eventually wrote the rules for the games.

Squash is played on an indoor court 18 1/2 feet wide, 32 feet long and 16 feet high. The ball is played off four walls. A match consisits of the best three out of five games, with each game going to 15 points.

Squash enthusiasts say the game is much more demanding than racquetball because the racquet face is smaller, the ball is harder the playing surface is smaller and the ceiling is off limits.

"When you find someone of exactly your own ability, it becomes a duel more intense than any you'll find in other one-on-one games," said a long-time enthusiast. "Because of the confined space, the speed and the immediacy of each play, your reflexes are everything."

The Washington Squash Racquet Club looks extravagant -- an imported English bar in the clubroom, oriental rugs and wing chairs, and pumpkin soup and quiche for lunch. But membership rates at WSRC, at 20th between L and M streets NW, are modest. Fees range from $75 a year (plus court time, which is $2 to $8 per hour) for individuals to as much as $500 for corporations.

Lane, 25, has been with WSRC since Sept. 1. He is ranked among the top five area players in the open division by the National Capital Squash Racquets Association, and has been number one in Virginia for three consecutive years.

Lane enjoys his teaching role at the club and is especially sensitive to the problems of beginners, which most of the members are. "Beginners are nervous. pI try to keep it light and remember it's new to them," he says.

Enthusiast Joan Challinor took up squash four years ago, at 48, after a severe case of tennis elbow forced her out of that game. "I think it's the greatest game ever invented," she says. "Compared to tennis, squash is like checkers and chess."

Challinor, who calls, herself "the oldest female player in Washington" says that five years ago, she probably could not have played the game here.

"The only places to play were clubs for men only," she says.

Other players who recently have taken up the game like the way it burns up so many calories in so short a time and the fact that the club is so convient for those who work downtown.

"It's great," one player says. "It takes 10 minutes to walk over here and five minutes to change. In a half-hour of squash I burn up what takes tennis players two hours."