Unfortunately for the somewhat improved Washington Capitals, the ground rules for playoff participation have been changed in this, their eighth season in the National Hockey League.

Instead of trying to beat out five of the NHL's lightweights, Washington must finish at least fourth in a five-team Patrick Division comprised mostly of heavyweights. The opposition consists of the Stanley Cup-champion New York Islanders, the semifinalist New York Rangers, the Philadelphia Flyers and the Pittsburgh Penguins.

The influx of underage talent into the NHL makes analysis difficult this year. Even those youngsters who have been impressive in exhibition games may find themselves overwhelmed by the increase in intensity that will accompany Tuesday's opening. One thing is certain , however: Washington is in for a long struggle.

That prospect does not dampen the ardor of Coach Gary Green, who welcomes the challenge.

"All summer in Canada, everyone was telling me, 'What a division you're in.'" Green said. "We're aware of it. We asked for it. The Islanders reign supreme, and they should, but I don't think we're all that far apart from a team like Philadelphia and we're every bit as good a team, if not better than the Rangers and Pittsburgh. Of course, that's fine and dandy to say, but we have to go out and prove it."

The Islanders, once Denis Potvin has regained his health, figure to roll to one last Stanley Cup before their payroll crashes in on their heads. Minnesota, with an easier playoff path, should once again be a finalist.

One of the more interesting aspects of the season is the attempt of Philadelphia, Minnesota and Boston to influence next year's No. 1 draft pick, certain to be winger Brian Bellows. The Flyers own Hartford's No. 1, the North Stars have Detroit's, and the Bruins have Colorado's. Each figures to help whatever team is likely to fall below its personal patsy.

Here is the prospective order of finish: PATRICK DIVISION

1. New York Islanders -- Potvin's severe groin pull assures a slow start; the yislanders always have slumped when their team leader is hurt. The goaltending is a possible source of trouble, too, with Bill Smith recovering from a broken finger. But rookie Brent Sutter adds firepower to a potent forward line and, overall, the rating is still No. 1.

2. Philadelphia -- Rick Mac Leish's 38 goals will not be replaced easily, but Ron Flockhart adds quickness.A key factor is whether defenseman Jim Waston is 100 percent following back surgery. The Flyers are a year away from a big jump forward.

3. New York Rangers -- Herb Brooks should bring discipline to a talented group that has everything else. The big question here is not the settlement of the Bobby Hull flap but, as the Capitals' Jack Button says, "Herbie puts so much pressure on himself; can he do it for 80 games?"

4. Pittsburgh -- The Penguins have good overall balance, except in goal. Coach Eddie Johnston, an old goalie himself, promises if Paul Harrison and Michel Dion can't do the job, the club is prepared to get someone who can. Age is a problem, but there are good young players -- Mike Bullard, Doug Shedden, Randy Boyd, Marc Chorney.

5. Washington -- Bobby Carpenter should fill some seats, but it will take another defenseman or two to provide a boost in the standings. Watch for a trade involving the Capitals' No. 1 pick for 1982 after the waiver draft is completed. ADAMS DIVISION

1. Buffalo -- Scotty Bowman, the best coach in hockey, is back behind the bench. Gilbert Perreault's broken ankle will slow things for a while, but the Sabres have excellent young talent, good balance on defense and superb goalending from Don Edwards and Bob Sauve.

2. Montreal -- New Coach Bob Berry is the latest brave soul trying to fill Bowman's vacated shoes. Already, there are signs of rebellion from the troops, so it should be a newsworthy season in the Forum. The Canadiens' defense is outstanding, but there isn't a lot of size up front and the goaltending is questionable.

3. Quebec -- The Nordiques have difficulties in the nets, with Dan Bouchard staying away from camp. An all-Stastny line sounds devastating, but newcomer Marian is not as talented as Peter and Anton. Jacques Richard is not likely to approach 52 goals gain and the defense is suspect.

4. Boston -- This is a combination of peach fuzz and gray hair. Barry Pederson and Steve Kasper are young, swift centers with ability. Brad Park, Wayne Cashman, Don Marcotte and Rogie Vachon are a bit long in the tooth.

5. Hartford -- This is the NHL's worst team and considering the strength of the divisionsal opposition, should be out of the running by December. NORRIS DIVISION

1. Minnesota -- The North Stars are lacking in toughness, but in this division it is not an essential quality. A good, young skating club, Minnesota has nowhere to go but up, particularly if goalie Don Beaupre can reapeat his sensational rookie year.

2. St. Louis -- The Blues led the NHL in improvement two years in a row, but now it is time for a dropoff. After the Rangers' playoff victory the Blues no longer can mask their defensive deficiencies, and the Canada Cup disaster left some questions about Mike Liut's glove.

3. Chicago -- The offensive-minded defense will produce a lot of goals. Teh doubt is whether Tony Esposito, at 36, can continue to make up for the defensive mistakes.

4. Detroit -- Coach Wayne Maxner has been cleaning house and this is one house that needed it. Greg Smith will strengthen the defense, but there may be too much pressure on goalie Giles Gilbert, who has been unable to handle it in the past.

5. Winnipeg -- The Jets should be much improved, with junior teammates Dale Hawerchuk and Scott Arniel moving up to the NHL on the same line. Ed Staniowski will fill the goaltending vacancy. New Coach Tom Watt is a good theoretical coach and figures to restore lost confidence among the returnees.

6. Toronto -- General Manager Punch Imlach's heart attack leaves club leaderless again. There seems to be an attempt to build another Broad Street Bullies group here, but it is at least five years too late. SMYTHE DIVISION

1. Edmonton -- The Oilers hve Wayne Gretzky and a lot of other youngsters who can skate and score. If goalie Andy Moog can match his playoff heriocs, Edmonton could be the surprise of the year.

2. Calgary -- The Flames are a big, physical team tailored to the tiny Stampede Corral, where they lost only five games last season. Hardy Astrom provides some depth in goal, a problem area after Bouchard departed last season.

3. Vancouver -- An injury to defenseman Harold Snepsts has tempered the optimism with which the Canucks star4ted camp. It wil be interesting to see how the aging Czechs, defenseman Jiri Bubla and center Ivan Hlinka, adapt to the NHL.

4. Los Angeles -- Disciplinarian Berry has been replaced by Parker McDonald, a hail-fellow-well-met. With owner Jerry Buss a player's pal, too, this club could be playing more beach volleyball than hockey.

5. Colorado -- Chico Resch and Phil Myre provide experience in goal and Bob Lorimer will help the defense, but the only other thing the Rockies have going for them is the altitude.