The Washington Capitals hope tonight's game in Philadelphia will be a playoff preview. If that sounds suicidal, it beats a slow death.

Sixteen of the National Hockey League's 21 teams will participate in the Stanley Cup playoffs, beginning in April and, somehow, ending in May. The first-round pairings, best-of-five series, will match No. 1 with No. 16, 2 with 15, etc.

The Flyers, 27-0-11 at this stage, seem likely to close the regular season on top of the heap. The Capitals, now 11-24-6, share 20th place with Colorado and realistically cannot expect to finish much higher than 16th. w

Should the Capitals, now seven points behind 16th-place Detroit, sneak into the final berth, they would open their first playoff competition with two games on the ice of the No. 1 finisher before returning home for that long-awaited first Stanley Cup contest at Capital Centre.

Since the regular season does not end until April 6, such speculation might seem premature. Coach Gary Green, however, has been talking playoff at every opportunity, knowing how easy it would be for his charges to lose their motivation and start thinking of the usual April vacation in Florida.

"We are going to be in the playoffs and when we get there we are going to be prepared," Green said. "We have been playing well at home, but that is not enough. To win in playoff hockey, you must play physical, intense games away from home.

"If we can do it at home, we can do it on the road. We did it in Minnesota a week ago and should have won, with any luck. We have to do it in Philadelphia, too. When we do make the playoffs, because of our difficult start, we will be playing a team like Philadelphia on the road."

So tonight, beginnning at 8 p.m. on WDCA-TV-20, Washington hockey fans may learn what to expect when those playoff games roll around.

Green scouted the Flyers Sunday as they played a 1-1 tie with St. Louis and maintained an undeafeated home-ice record that now includes 16 victories and six ties. Presumably, Green will try to match lines in the fashion of recent games, making minor adjustments in his usual alignment to attain maximum man-on-man effectiveness.

It will take some dedicated checking to derail the Flyers' No. 1 line of Brian Propp, Bobby Clarke and Reg Leach.

Propp, Philadelphia's first draft choice, has 21 goals and 20 assists, by far the best mark by a rookie. Clarke, now an assistant coach, has scored only six goals while passing off a remarkable 32 assists. Leach, once dangled through the NHL as trade bait, is the club's high scorer with 27 goals and 18 assists.

Although the Flyers used speed more than intimidation in compiling their record 35-game unbeaten streak, they still rank second to Vancouver in penalties. Paul Homgren, with 152 minutes, is among the league leaders and Mel Bridgman, Behn Wilson, Moose Dupont and Jack McIlhargey will never be contenders for the Lady Byng trophy.

Goalie Pete Peeters is still unbeaten, with 15 victories and five ties. Peeters, who will win rookie honors if Propp does not, is the fourth goalie in NHL history to post a 20-game unbeaten streak, following Frankie Brimsek, Gerry Cheevers and Chico Resch. Peeters has a 2.56 goals-against mark, compared with the 3.50 of veteran Phil Myre.

Philadelphia is one of three NHL teams the Capitals never have beaten. The series includes 16 Flyer victories and four ties, with the Spectrum figures a perfect 10-0 and a 60-20 edge in scoring.

Defenseman Rick Green, plus 10 in his last seven games, is a questionable starter for Washington tonight because of the right hand he damaged while decking Duane Sutter of the Islanders . . . Hershey, with an acute goalie problem, opens a four-game road trip Wednesday in Glens Falls, N.Y., against the Adirondack Red Wings. It would be no surprise if Gary Inness went along to get some needed work . . . Tom Rowe has scored only one goal in his last 15 games . . . Robert Picard was on the ice for all five Islander goals in Washington's 5-2 loss . . . The Capitals entertain Edmonton and Wayne Gretzky Wednesday night.