It has been apparent since the season began that the Washington Capitals would be in trouble should the club's inexorable injury jinx strike either Paul MacKinnon or Rick Green, the two pillars of the defense.

Trouble came Thursday night, when MacKinnon went down in the first period in Denver with what appeared to be torn collateral ligaments in the right knee. MacKinnon flew back to Washington this afternoon and was admitted to Arlington Hospital, where Dr. Pat Palumbo was scheduled to examine him and perform surgery, if necessary, on Saturday.

An operation seemed likely, considering the wobble in the knee.

"I'm hoping the kid gets lucky and it's not a tear, but I'm afraid there's not much chance," said trainer Gump Embro. "We haven't had much luck with knees and this doesn't look good."

Left wing Paul Mulvey was injured in the same game, taking a cross check to the left side. Although X-rays showed no rib damage, there was fear of internal injury and Mulvey was not expected to play in Saturday night's game here against the Edmonton Oilers.

Defensemen Darren Veitch, strained left knee, and Green, bruised left hand, also were banged up in the Denver contest. The final indignity was supplied by the Colorado Rockies, who scored twice in the last two minutes and tied the Capitals, 5-5.

To replace MacKinnon and Mulvey, the Capitals today called up defenseman Howard Walker from Hershey of the American Hockey League and left wing Torrie Robertson from Victoria of the Western Junior League.

Walker was with the Capitals the first week of the season, although he did not play. A member of North Dakota's NCAA champions, he was signed as a free agent during the summer.

Robertson, a third-round draft choice, made the team in training camp as a fourth-line left wing. However, it was decided to send him back to Victoria for his final junior season rather than have him sitting on the bench much of the time. He can play 10 NHL games without forfeiting his junior eligibility.

Complicating the defensive picture is the condition of veteran defenseman Yvon Labre, who underwent knee surgery a year ago, ironically following a game here in which Pete Scamurra also was disabled.

Labre's right knee has not responded as well as had been hoped. It still contains some bothersome fluid and he is lacking mobility. Labre played back-to-back games against St. Louis last week, but was benched much of the second contest when he was obviously laboring.

Coach Gary Green held Labre out of Wednesday's game in Los Angeles, hoping that he would be ready for a top effort in Denver Thursday.Although Labre saw considerable action because of the injuries to MacKinnon and Veitch, he was not skating with the necessary mobility.

"It is bothering me," Labre said. "There is some fluid on it, but the doctor says there isn't enough to draw it off right now. I worked with the weights in L.A. and it felt a little better, but I know it's not what it should be."

MacKinnon, who missed 17 games last season with a fractured cheekbone, had been the team's steadiest defenseman, compiling a plus-four rating. He was hurt in a melee in front of the Washington net late in the first period.

"There were three of us bumping near the net, I think Yvon (Labre) and (Lucien) DeBlois were the others," MacKinnon said. "My foot was stationary and I got hit from outside in."

Embro was working on MacKinnon in the dressing room when he heard a roar and rushed out to see Veitch lying along the boards. He had been racked up by Colorado's Randy Pierce.

Veitch was able to return to action in the second period, wearing a brace on the knee after a combination of tape and the brace proved too restrictive.

"The shock syndrome when Mac went and then Darren went, you couldn't believe the atmosphere," Gary Green said. "I found myself saying, 'Oh no, not again.' They were scared, the guys going down boom boom and the doctor working on guys left and right.

"They really got a lift when Veitch came back. You could see everybody buzzing about the kid. It really tells you what kind of a kid he is. He knew we were hurting and he got back out there, even though you knew it was bothering him."

"There was a little pain every stride, but other than that it's okay, I guess," Veitch said. "Gump told me I could go back to Washington and have it checked, but I don't want to miss those games in Edmonton and Winnipeg."

Veitch is a native of Saskatoon, Saskatchewan, and played his junior hockey in Western Canada with the Regina Pats.

Alan Hangsleben, a defenseman when he played for Hartford who has played at left wing for Washington, was moved to the backline after MacKinnon and Veitch were hurt. However, Green was still uncertain, pending a comprehensive examination of Veitch's knee, where Hangsleben would play Saturday.

"I'm still at the pen and napkin stage," said the coach, doodling over possible combinations. "I've had lots of practice at it.

"We'll regroup. We won't hang our heads and throw in the bucket. We have a lot of fine hockey players here and the worst thing we could do is start feeling sorry for ourselves. These injuries are tough to take, but they're part of the game and you have to take them."

Shortly after Green became the Capitals' coach a year ago, the team had 11 players out with injuries and most of the farmhands from Hershey took turns wearing Washington uniforms.

Center Guy Charron did not play Thursday, because of a bone bruise in the lower back. He tried to skate in the warmup, but was unable to maneuver properly. He was X-rayed here Thursday night, with negative results.

The Capitals can expect no sympathy in their next two contests, here on Saturday (WTOP--1500 at 8 p.m.) and Sunday in Winnipeg (8:30 p.m.). Edmonton, with a 2-4-3 record, is coached by former Capital defenseman Bryan Watson and Winnipeg is guided by ex-Washington Coach Tom McVie, who has not been able to beat the Capitals since moving west.