The New York Islanders will be trying to rid themselves of one of sports' more notable inferiortiy complexes when they battle the New York Rangers in a best-of-seven Stanley Cup semifinal series opening tonight at Nassau Coliseum.

Meanwhile, the National Hockey League defending champion Montreal Canadiens will be hosting the Boston Bruins, the team they whipped in the finals the last two years.

The Islanders have finished ahead of the Rangers four straight seasons and this year posted the best overall record in the NHL, 51-15-14. They beat the Rangers in five of eight regular season games and, in the only previous playoff series between the teams, in 1975, the Islanders ousted the Rangers in a three-game preliminary round. Still, the Islanders do have that feeling of being a wormy No. 2 in the Big Apple.

"We're not even No. 1 in New York," Islander defenseman and assistant coach Bert Marshall said. "The Rangers own this area. No matter how poorly they play, they're still the team from New York.We're just a team from Long Island. And where's Long Island?"

Anyone without orienteering experience who has tried to locate Nassau Coliseum a first time would be hard pressed to answer that one. But anyone with the slightest interest in hockey knows about Bryan Trottier, the league's leading scorer, 69-goalman Mike Bossy and Denis Potvin, the league's best defenseman. They have lifted a team that won only 12 games in 1971-72 to one that is considered an even bet to end Montreal's three-year reign as Cup champion.

The tendency to root for the under-dog is muted in this circumstance, because virtually everyone outside Boston and the Madison Square Garden combat zone with any regard for hockey is eagerly awaiting a Montreal-Islanders final.

That showdown can be expected as long as those two teams do not start thinking of each other before completing the necessary preliminaries. A year ago, the Islanders took Toronto too lightly in the quarterfinals and went no farther.

"They were overconfident and maybe they didn't work hard enough," said Islander Coach Al Arbour, looking back on that shocking experience. "The thing is, these guys are thinking about last year. You learn from everything and hopefully, they learned from that series."

The Islanders have been resting since Sunday while the Rangers were completing the only five-game quarterfinal by beating Philadelphia, 8-3, Tuesday. Ranger defensemen Dave Maloney (severe charley horse in his right leg) and Ron Greschner (bruised shoulder) were banged up in that most physical battle and the Rangers are in below-par condition.

"You can't tell what's going to happen in the playoffs," insisted Ranger veteran Phil Esposito. "One day you can play a 10-10 game and the next day it'll be 1-1. The Islanders have a good club and we'll really have to forecheck, play our best to beat them. I'm looking forward to a tough, good hockey series. They play hockey, we play hockey, and I don't expect any cheap stuff."