There will be no feeling-out period Tuesday night when the best-of-seven Stanley Cup final opens at Nassau Coliseum.Both the defending champion New York Islanders and the first-time challenging Minnesota North Stars have thrived on early haymakers.

The Islanders scored the first goal in eight of their 13 playoff games and won all eight. New York, the regular season winner, is a superb forechecking team that is difficult to handle once it moves in front. Trailing opponents have found it a trying task merely to carry the puck into the offensive zone, much less set up for testing shots.

Minnesota, as the ninth-place finisher, has not been gifted with homeice advantage in any series. The North Stars, however, quickly removed that obstacle by capturing the opening games in Boston, Buffalo and Calgary. They never fell behind there after in recording three straight upsets.

This figures to be a familiar hockey matchup of the 1980s. A quinella betor could do worse than tout these teams as the finalists once again when the new season starts in October, because, with the upcoming realignment, it will take a combination in injuries and surprises to chop them down to competitors' size.

The Islanders undoubtedly are the best team in the National Hockey League. They have a great scorer in Mike Bossy, 24, who received the computerized Seagram Award yoday as the best in hockey; probably the sport's most talented all-round player in Bryan Trottier, also 24; a fine rushing defenseman in Denis Potvin, 27, and the best power play and penalty killing units in the NHL.

New York is No. 1 in the checking department, too, and that is the area where Minnesota, riddled by injuries all season, probably will be at the greatest disadvantage. Clark Gillies, Bob Nystrom, Dave Langevin, Trottier and Potvin all are heavy hitters and they have been restoring their strength for the past week while the North Stars were disposing of Calgary.

"The Islanders are big and strong and they follow through on their checks," said Washington General Manager Max McNab. "Our medical staff is busier and our players are hurting more after an Islander game than any other."

Is there is any hint of a weakness in the Islanders' armor, it is in goal, where Bill Smith, 30, has been forced to carry so much of the load. Smith has thrived on the work, building a 2.25 goals-against mark in 12 playoff games, but should he be hurt -- and he plays a scrambling game that is conducive to injury -- the Islanders could be in trouble.

Of course, with so prescient a general manager as Bill Torrey, it is likely there will be another top-flight goalie in the fold before a new season begins. Torrey dealt unhappy veteran Chico Resch to Colorado at the March trading deadling for defenseman Mike McEwen and many so-called experts asked, what do the Islanders want with McEwen?

Then Stefan Persson broke his jaw early in the playoffs and McEwen stepped in to earn 11 points in 12 games and become a key figure in a power play that already has set a one year playoff mark by scoring 26 times.

Minnesota is a likely finalist in years to come by accident of geography, rather than through overpowering talent. The North Stars have been assigned to the weaker western half of the new alignment, and they will be battling St. Louis, Los Angeles and Calgary for finalist status, while the Islanders chop their way through the likes of Philadelphia, Buffalo and Montreal.

This observation is not intended to denigrate the North Stars, though. Under the dynamic leadership of Lou Nanne, Minnesota is one of the franchise of the future. Several weeks ago, the enthusiastic young North Stars decided they would not shave until they won the Stanley Cup or were eliminated; the club had a policy of no beards, but as Coach Glen Sonmor noted, it was no real problem making an exception.

"Some of our guys are so young, you'll need a month before you notice they haven't shaved," Sonmor said.

Steve Payne, 22, was the best left wing in the NHL a year ago and, after slipping a bit during the past season, he has been a playoff standout with 12 goals and 22 points, second only to Bossy's 13 and 27.

Bobby Smith 23, has recorded 20 points in 14 playoff games; Dino Ciccarelli, 20, has netted 11 playoff goals, a rookie record, after hitting for 18 in 32 regular-season games; Brad Palmer, 19, has seven goals in the playoffs, a surprise for a kid whose postseason action was expected to be served with the Victoria junior team; goalie Don Beaupre, 19, has won all three playoff starts, although Sonmor has given veteran Gilles Meloche most of the pressure assignments despite Beaupre's better seasonal marks.

Besides this nucleus of talent, add Olympians Steve Christoff and Neal Broten, plus outstanding young defensemen Craig Hartsburg and Curt Giles, and note the fact that Minnesota, as a result of dispensing surplus talent from the merger with Cleveland, has five selections in the second round of the June amateur draft. Those North Stars are shinning bright.