Michel Bergeron, the Ranger coach, said the decision to sign Lafleur was based not on his laurels but on a performance in training camp in which he outshone veterans like John Ogrodnick as well as several youthful prospects. Happy Camper

''We all agreed that Guy was one of our best players at training camp,'' said Bergeron, who declined to estimate the goal-scoring impact Lafleur could have. ''We all remember Guy Lafleur as a 50-goal scorer. I don't honestly think he's going to score 50 goals for us, but I said before camp that if he was one of the best 24 players he was going to make the team, and he made it.''

Lafleur sought a tryout with the Rangers this summer after being turned down by the Los Angeles Kings, who decided they would look within their organization to find a right wing for Wayne Gretzky.

Esposito, who is gaining a reputation for having a restorative effect on disenchanted and disenfranchised hockey players, admitted he was skeptical about Lafleur's abilities only until he watched him perform at training camp. Instead of figuring he had nothing to lose by indulging Lafleur in his comeback campaign, Esposito began to think the former superstar might actually enhance the club's playoff hopes. Esposito Is Impressed

''After watching him closely, he may consistently have been our best forward,'' said Esposito, who has the option of re-signing Lafleur, with a 15 percent raise, for next season. ''He brings a winning attitude to this club. When you've got a talent like Mr. Lafleur has, well, maybe it's not as great as it was at 21, but maybe it is. We'll just have to wait and see.'' Lafleur was 11th on the career goal-scoring list with 518 goals, 14th in assists, and 11th in overall scoring with 1,246 points when he left the league.