On April 3, two days before the close of the National Hockey league season, the New York Rangers defeated Chicgo to clinch a berth in the Stanley Cup playoffs. Both fans and players rejoiced in fashion more suitable to a first-ever appearance by the Washington Capitals than to a last-gasp entry by a slipping team that two years before had reached the Cup final.

Now that the Rangers have eliminated fourth-place los Angeles in four games and have built a 3-1 lead over second place St. Louis, the potential exists for a celebration of volcanic proportions.

If the Rangers beat the Blues, and they have three chances to finish off that series, starting with tonight's contest in St. Louis, and if the New York Islanders eliminate Edmonton -- the circumstances are similar, with tonight's fifth game on Long Island -- the two New York teams will meet in semifinals.

Two years ago, the Rangers upset the Islanders in a six-game semifinal that enabled some scalpers to alter vacation plans from Jersey Shore to European spas. Now, with the Islanders having won the Stanley Cup in the interim and the Rangers carrying on like Cinderella, a shootout between the two would be that much more dramatic.

Anticipation has whetted New Yorker's appetites for the rematch. When the Rangers achieved playoff status, there was reason to believe they might finish 15th and the Islanders second, creating an immediate confrontation. The Rangers, however, scored an implausible final-night shutout victory in Philadelphia to climb to 13th and the Islanders overhauled St. Louis to finish first.

Then, the Rangers' preliminary-round success was accompanied by 14th-place Edmonton's wipeout of Montreal, so the Oilers got the next crack at the Islanders. Despite some gutty play by Wayne Gretzky and friends, Edmonton's bid for another shocker foundered Monday night when Olympian Ken Morrow's overtime goal boosted the Islanders within one victory of advancement.

Meanwhile, the Rangers were handling the Blues with relative ease, killing off eight straight St. Louis power plays in a 4-1 romp marred only by a knee injury to right wing Eddie Johnston. He suffered ligament damage and is out indefinitely. The Rangers' physical play, led by captain Barry Beck, has been too much for the weary Blues, who were forced into double overtime in a fifth preliminary-round game against Pittsburgh before opening the Rangers series two nights later.

Another team that needed five games for a first-round decision, Philadelphia, has shown the effects of the gruelling schedule, which required each quarterfinalist to play four times in five nights. The Flyers have dropped three straight to Calgary and could disappear as early as tonight, when Game 5 is scheduled for the Spectrum.

The flames, outshot in all three victories, have been blessed with some remarkable goaltending by Pat Riggin, whose 3.83 regular-season goals-against mark enabled Rejean Lemelin to assume No. 1 status. The current success of the Flames is in direct contrast to previous seasons, since they never won a playoff series in six tries while based in Atlanta.

To show how much things have swung in the Flames' favor, the unlikely hero in Monday's 5-4 victory was winger Randy Holt, who scored twice in the third period. Holt had never before produced a playoff goal, boasted only two in 236 regular-season games and this year was assessed 165 penalty minutes while failing to score.

If Calgary advances, its likely opponent is Minnesota, which carries a 3-1 lead into Buffalo tonight.