There is an old adage in sports that the way you practive is the way you play. If everyone believed it, Bob Sirois would be a chef in his native Montreal.

Instead, Sirois is the Washington Capital's leading goal scorer, with 17. More important, he is one of the best two-way players in the National Hockey League.

The NHL dreamed up a new plus-minus system this year, so folks could compare players on different teams. It rates a player's on-ice presence during equal-strength goals, for and against, as percentage of his team's figures.

After 20 games, Sirois ranked ninth in the league at plus 14-6 per cent, despite a raw minus-four figure. Since then, he has played superbly, lifting his old-style mark to plus six and his newfangled percentage to plus 21.9. Only two players, Clark Gillies and Bryan Trottier of the New York Islanders, topped that figure in the 20-game compilation, the latest released by the league.

Although he and Bill Riley became the Capital's first plus players last season, the oft-injured Sirois was given a difficult time by management during training camp at Hershey and wondered whether he even would be with the team for the opener. The complaint was that he wasn't working hard enough.

"I'm terrible in practice," Sirois admitted. "I can't put my mind in game condition. In a game you have to react right away. In a game it's rare to think, you use intuition or something. I like that, doing the play as it comes. In practice you have to execute set moves and I find it hard to concentrate on them.

"I concentrate a lot before a game, but not in practive. Or training camp, either. Training camp really shook me up. I kind of had a feeling like I wasn't part of the team at all. It made me work a lot harder. I was worrying about my job. I still do."

At least Sirois, a deceptively fragile 6 feet and 175 pounds, has been able to stop worry about injuries. In 1976, after he was obtained from Philadelphia'a Richmond farm club, he suffered a bruised kidney and was unable to finish the season. Last year he missed the first month with strained knee ligaments, sat out another month with a broken thumb, was idled a third month by torn shoulder ligaments, then missed two weeks with a back injury.

"The first year and a half here my head was unsettled by the injuries," Sirois said. "On the ice I'd be more aware of being injured than anything else. Even though I built my body up during the summer, I was still concerned the first couple of months this year, because I'd never played more than 20 straight games.

"But I got hit pretty hard and often and still by mid-December my body was in good shape, so I stopped worrying. Lately I've had a few muscle problems, but they're nothing after my troubles last year."

Sirois derived on benefit from all that injury time. He got to watch his teammates.

"I picked up a lot of things watching them." Sirois said. "Guys like Billy Collins were always coming back, looking for a man there. It's helped me get more involved in the defensive part. I always take a look to pick up my man. If we don't have the puck, I try to pick up somebody."

The Buffalo Sabres, who visit Capital Centre tonight at 7:30, feature the French Connection of Gil Perreault, Richard Martin and Rene Robert, the latter just out of the hospital after treatment for back spasms. Despite the fame of that trio, all ranked below Sirois on the NHL's plus-minus chart.

Washington has its own French line - Sirois Guy Charron and Bob Girard - and Sirois was asked if there was any attempt to imitate the slashing Sabres.

"Our line has been playing great and doing a lot of things right," Sirois said. "But Perreault's line, we're a mile behind them. You can't even compare us as individual players. The Perreault line is always checked closely. They've started to check us a little bit, but the other teams still act as if they don't believe it. I hope we don't get checked like that.

"Just playing against those guys, and playing in the NHL, is a great feeling. I feel like a young rookie. I never feel I'm a star. My goals come from a lot of hard work by four other guys and also a lot of luck."

Modesty aside, they also come - five in the last five games - from his ability to shoot from any angle. In fact, it has been Sirois' adaptability, playing either wing, that has made him so valuable as teammates were chopped down by injuries this fall.

"The name of the game is trying to score," said Sirois, a lefthanded shooter. "Each time I get the puck in the other team's end I try to put the puck on net. Most goals are scored on plays when you're not supposed to score. There aren't many picture goals. The more you shoot, the more chances you have to score.

"It's the same game at left wing or right wing. From the right side I see the game better, I don't know why. On the left side I'm more capable of making plays. I don't have much confidence in my backhand poss, so on the left side I'll usually try to make a play, while on the right side I'll carry the puck."

Sirois seems likely to be picked as the Capitals representative in the Jan. 24 All-Star Game at Buffalo, but he doesn't consider himself qualified.

"I don't really think I should be," Sirois said. "There are so many good players in the NHL. If I should be chosen, I won't feel I belong there. Other players are playing half as much - I'm lucky to get so much ice time here - and scoring as much and playing as well. Look at Terry O'Reilly in Boston. He's never been in one. He should be picked before me."

Such self-effacement leaves Sirois no future as a politician, but when he hangs up the skates in what Washington fans hope is the distant future he can always become a chef. Roommate Robert Picard risked his mother's wrath by saying, "Bobby is the best cook I know." And, just in case he loses his culinary touch, Sirois has insurance. He and Girard own a restaurant in Montreal.