The Philadelphia Flyers have extended the contract of Coach Paul Holmgren, reportedly through the 1992-93 season, despite the club's unaccustomed cellar finish in the NHL's Patrick Division.

Bobby Clarke's successor as Flyers general manager, Russ Farwell, said in his three weeks on the job he found that Holmgren "has the total respect of the players and the leadership qualities that I believe are right for this team." . . .

Chris Nilan, who often aggravated Boston players with his physical style, today is a Bruin -- via a trade of right wing Greg Johnston and future considerations to the New York Rangers.

Nilan, also a right wing, adds tough checking to a team that lacked an enforcer last season when it swept Washington to reach the Stanley Cup finals only to lose in five games to Edmonton.

A Boston area native, in 11 NHL seasons he has a high of 21 goals in 1984-85 with Montreal. Knee and arm injuries limited him to 25 games last season (one goal, two assists). Johnston, 25, is seven years younger. . . .

Washington Capitals' draft choices John Slaney (defenseman, first round) and Brian Sakic (right wing, fifth round) have been invited to the Canadian Junior National team training camp. They'll compete there, Aug. 16-23 in Saskatoon, Saskatchewan, for places on the squad for the world junior tournament Dec. 26-Jan. 4, also in Saskatoon.