Defenseman Yvon Labre, the original Capital, will undergo surgery this morning at Arlington Hospital to have torn cartilage in his right knee repaired.

Labre, who will be 30 Thursday, had an operation on the same knee in November 1977 and it was feared his career might be over. Instead, after two tours in Hershey, he returned to finish the season by recording points in the team's last four games.

Last year, although he missed nine weeks with a dislocated shoulder, Labre had his finest season as a professional, closing with a plus-eight rating that was the best ever recorded by a Washington defenseman.

Nevertheless, this season Labre found himself forced to scramble for a starting job on a team with nine experienced defensemen. After sitting out the first two games, he moved into the lineup for the Oct. 14 victory over the New York Rangers and convinced everyone that he belonged. His current rating is plus two.

Early in November, Labre noticed a buildup of fluid in his right knee. He continued to play but, after taking two hard hits in Colorado a week ago, limped out of McNichols Arena and decided it was time for a definitive examination.

Even though torn cartilage was the diagnosis, Labre tried to continue playing. He participated in a grueling workout Friday without complaint, but it was apparent he lacked the necessary acceleration and the decision to operate was made yesterday.

The Capitals' corps of injured regulars was reduced to six when winger Bob Sirois was given the okay to play against Toronto here Wednesday. Sirois has played in only one game since Oct. 20, when he strained back muscles.

Winger Tim Coulis was assigned to Hershey yesterday, his third trip to the minors in 10 days. Coulis was pointless in five games with Washington.