After purging the nonphysical half of their Scandinavian contingent, the Washington Capitals prepare for a major test of future possibilities with the arrival of the New York Islanders for a 7 o'clock contest tonight at Capital Centre.

Left wing Antero Lehtonen was paid off yesterday and is free to negotiate with another NHL team, return to Finland or contact other European clubs. Arrangements were also completed for defenseman Leif Svensson to return to his old Swedish team, Djurgarden, although he may be called back should the Capitals be hit by injuries.

In each case, the players were not physical enough to suit Coach Gary Green, who prefers his European players -- and all others -- in the mold of soled checkers Rolf Edberg and Bengt Gustafsson. Green will be calling those shots for a long time, too, because the Capitals confirmed yesterday that Green has received a two-year contract extension, through June 1983.

There was leftover elation at the Centre after Friday's decisive 4-1 conquest of Winnipeg. It must be remembered, however, that the Jets tied for last in the 21-team NHL; tonight's guest won the Stanley Cup.

The presence of Denis Potvin, Bryan Trottier, Mike Bossy, Clark Gillies and -- lest we forget -- Gord Lane promises to add another element to the education of the kind of player Green prefers, the No. 1 draft choice, defenseman Darren Veitch.

Veich was warned to expect a difficult time with the swift-skating Swedes on the big ice in Stockholm and he was advised to be ready for a big boost in tempo between the last exhibition and first regular-season contest. In neither case was he awed or overmatched. Now he must prepare for the best team in the NHL and that does not seem likely to unsettle him, either.

" had no problems at all last night," Veitch said, "but I know the Islanders will be a lot tougher. They're going to play a different game. They'll take the body and they'll still skate very well. I'm looking forward to it. It's easy to get up for this game."

Green has been pleased with Veitch's steady development, but he intends to take it slowly, at least for the present home stand. On home ice, Green has the advantage of last change and he does not intend to match Veitch against players like Trottier and Bossy, except "maybe for one shift to see his reaction.

"Darren played a very steady game last night and we know there are far better things to come," Green said. "We aren't going to initiate the guy against the fastest, strongest players on the other club .

"In the past the first draft choice was brought in here to be a savior. We're trying to bring Darren in through the back door, without too much pressure. In the past, the No. 1 had to go up against the best right from day one and that can be a terrible burden."

Veitch has needed to make adjustments from junior hockey. The speed of the game is a major change, with the NHL ranking somewhere near the Preakness, as compared to a claiming race at Timonium. In junior, Veitch was able to pace himself and control the tempo of the game; it is not an easy habit to break.

"The speed of the game is hard to adjust to and toughness is a big change, too," Veitch said. "All these guys are strong. I have to move the puck quicker, because they're on you right away.

"In junior I played 45 or 50 minutes a game and I guess I paced myself even if it wasn't done consciously. Here they tell me to go all out on every shift and get off. In a way that makes it easier. It's nice being paired with Pat Ribble, too. He's been playing well and he's very quick."

"I told Darren just to take a 30-second shift, concentrate on what to do and get off," Green said. "In junior he had the ability to speed a game up or slow it down. He can't do that here. He's such a smart kid that he realizes it and he's concerned about it. It takes patience on my part and on his part.

"Our expectations of Darren, his strengths and weaknesses, have held up pretty well. He's shown us what we read before. His strengths and passing the puck with great accuracy, shooting and smartness. He needs to adjust to the tempo of the game, the speed of the game and the strength of the players he is competing against.

"I hope the fans will realize he is just a 20-year-old if he makes a mistake, although there certainly was no problem last night. If a forward makes a mistake, a defenseman can cover up; if a defenseman makes a mistake, it's in the net."

Veitch inevitably will be compared to Robert Picard, who was dealt to Toronto for Mike Palmateer after Veitch was drafted. Green has done everythin possible to steer clear of such a comparison.

"I know he (picard) was a good defenseman," Veitch said. "Maybe half a year or a year from now I can take his place. They've never put pressure on me that way, but maybe the fans will.

"So far everything has been going well. It's hard, but I never thought it would be easy."

If Veitch has been upset by anything, it is the subtle threats of hazing by veterans. Rookies often find themselves shaved, either the head or elsewhere, and Veitch rarely accompanies team-mates anywhere without hearing a few whistled bars of the Gillette song.

Perhaps he has some reason for apprehension. Two of his present team-mates, Rick Green and Dennis Maruk, were members of the London Knights, who pulled one of the more memorable hazing gags on rookie Dwight Schofield. They tied Schofield, completely naked, on a chair, put him in the elevator of an Ottawa hotel and pressed all the buttons. Candid Camera never could match the expressions of the folks who boarded that elevator.

The fans admired the efforts of Veitch and his teammates Friday, but they were less satisfied with another rookie, public-address announcer Dave Fox. Fox has the unenviable task of replacing popular five-year veteran Mary Brooks, dismissed by the club last week. When Fox twice referred to Jean Pronovost as "Provonost," fans began chanting "We want Marv" and they enlisted the services of the San Diego Chicken as a cheerleader.

Brooks was bounced for refusing to wear a tuxedo to the games. Apparently, he thought he was employed by the Capitals, not the Pittsburgh Penguins.