With proper respect to Guy Lafleur, the principal reason for the Montreal Canadiens' three straight Stanley Cup victories is the presence of three big, strong defensemen - Larry Robinson, Serge Savard and Guy Lapointe.

The Washington Capitals are a long way from Stanley Cup contention, but it is not insanity to dream of future success. For the Capitals, too, are blessed with three big, strong defensemen - Robert Picard, Rick Green and Leif Svensson.

The pairing of the 6-foot-3, 211-pound Green and the 6-3, 190-pound Svensson has been the brightest happening of the Capitals' preseason preparation. They were superb in victories over Pittsburgh and Quebec. When they were given Sunday night off in Springfield, the Capitals' passing was way off too, and Washington lost to the New England Whalers, 5-1.

"It looks like they pair up well," said General Manager Max McNab. "They both pass so well, they complement each other. Whenever they got the puck in Quebec, it seemed like it wound up with a shot at the other end. And they really made our power play go."

Coach Tom McVie could look upon their absence as reason to discount the loss to New England.

"They had two great games," McVie said. "This is the time to take a look at other people. They deserve a night off so we could look at six other defensemen."

Green, no longer black and blue, is moving the puck and moving oppostion bodies, both with unaccustomed confidence.

About all Green has known during his first two National Hockey League seasons is the presence of pain. He suffered a broken right wrist and missed 35 games in his first campaign, after being selected number one in the entire amateur draft in 1976. Last season, he sat out of games with strained ligaments in that wrist and with a separated left shoulder.

"I worked at everything in the summer," Green said. 'The shoulder and the wrist are back to normal. I can play without tape, without a brace. I'm a little more confident about doing things now.

"I was playing sore all the time and I had some pain, so I was hesitant about taking certain knocks. I was afraid of hurting something again and missing more games."

Green added muscle during summer workouts, building his weight up to an all-time high of 211, which he believes he can carry comfortably. Along with his freedom from pain, it has made hime more physical in the corners. During the Capitals' first loss to the Whalers, he even exchanged bumpy greetings with 50-year-old Gordle Howe.

"Old Gordie, I watched him dozens of times on TV," Green said. "I never thought I'd see him out on the ice, play against him. So I figured I'd at least run into him, let him know who I was.

"When I checked him into the boards, he asked me. 'Are you new?' I just looked back and said. 'No, are you?' Then I said, 'Come to think of it, I think I've seen you someplace before.' He just chuckled."

Although a resounding success, Green's pairing with Svensson has required adjustments.

"He's smart with the puck," Green said, "but their style is a lot of circling in their own end to get a play started. Here, we're always trying to move the puck forward, so we don't get caught in our end. He moves the puck well and he's a heady player so we'll work things out."