It wasn't a walk on the sunny side of the street. Redskins wide receiver Art Monk knew that long before Washington's 28-0 victory over the St. Louis Cardinals yesterday. He knew it Thursday when he felt his little toe turn sideways, as if coming unscrewed.

He was running a pass pattern. He's run patterns for seven years without missing a practice or game. This time, the little toe gave way on a cut. "I was in pain the rest of the week," he said.

On Friday, a defensive back stepped on the toe in practice. "That irritated it more." Yet Monk continued to work out. X-rays of the right foot that night showed a hairline fracture. Although a layman might wonder what a man is doing running around on a broken toe, the team doctors said it wasn't bad. Offensive guard Russ Grimm is playing with two stress fractures in his left leg. Joe Gibbs, the coach, said the doctors told him there wasn't any risk in using Monk yesterday.

For his part, Monk said pain comes with the territory. It wasn't such that he couldn't play. "I really wanted to play." A championship was available at RFK Stadium. A championship for the Redskins, of all people. Not Dallas, not the 49ers--the Redskins could win a championship no one dared imagine within their reach. He wanted to play, as he had for four years at Syracuse and three more here.

Then, running a deep pattern on the Redskins' sixth play, Monk felt the toe go again. "A little pop." He ran another 20 yards on the broken toe. He dived for a long pass that fell loose only when he crashed onto the turf. It was his last play of the Redskins' wonderful season, and later he came to the bench on crutches, a forlorn figure in slacks and his No. 81 jersey.

"It's frustrating and disappointing," Monk said afterward, a cast on the foot. "Now that we're at this point, I'm suddenly out of the picture . . . All I could do is what I did: come to the bench and cheer for my teammates."

Janus had two faces. His month, January, is for looking back and looking ahead. Art Monk's 35 catches this season, the flamboyant ones deep as well as the gritty ones in traffic, were the cornerstone of the passing game. If we say these Redskins worked magic in winning the National Conference championship, we must bow in Monk's direction--and, looking ahead, we must wonder what his absence will mean in the Super Bowl tournament.

"You want to know what I think?" said Charley Taylor, the receivers coach. "I just came back from the bathroom, throwing up. That's what I think."

Around the locker room, everyone said Monk was important. He plays five offensive positions. He goes long, he goes over the middle, he carries on end-arounds, he even blocks at the line on short-yardage situations. Everyone said Art Monk is important, and everyone also said the Redskins will win without him.

"The things Art does, we'll use two or three people to do," said Dan Henning, the Redskins' assistant head coach. "That's one of the great strengths of this team. We have intelligent people and they'll pick up everything quickly.

"We'll move Charlie Brown from one side to the other, Nick Giaquinto will move around some, then Rick Walker has to run some routes Art normally would, and Rich Caster will fill in. At Charlie Brown's spot we'll have Virgil Seay and Alvin Garrett."

Which is wonderful in theory, and could be delightful in execution. But a look at cold facts gives pause.

Giaquinto, Walker, Caster, Seay and Garrett have caught a total of only 21 passes this season.

"We will still have success with our passing game," Brown said. "Without Art, I will receive double coverage, and that will free up someone else."

Joe Washington: "When we get to the 20, we have run a play called 'Fade.' Art is 6-2 and 210, and he runs into the end zone and Joe Theismann throws it up in the air for Art to go get with his leaping ability. We'll miss that down there. But overall we can use two or three people to do Art's job and they'll take up the slack."

Yesterday's victory was forgettable. The Cardinals were gawdawful. We will not describe in detail their incompetence. Children may read this. But the victory is unforgettable for what it says of the Redskins' work the last two seasons.

Bobby Beathard, the general manager, has worked a wonder. On Oct. 4 of 1981, the Redskins had lost 10 of 13 games. How could Beathard build a team when George Allen had sold its future down the Potomac? With low-round draft choices and free agents, Beathard did it so well that someone took blue ink to the locker room bulletin board yesterday: "NFC Champs."

Beathard's first No. 1 draft choice was Art Monk.

In a whisper of doubt, the Redskins' coaching staff let reporters know, "Monk's a half-step slow."

That coaching staff is now gone.

And now Beathard, who led Joe Gibbs into the view of owner Jack Kent Cooke, was in the locker room, taking congratulations and saying, "We have guys with great character and they'll step in and take up the slack from Art's absence."

Anyway, there is the Redskins' defense, which for three weeks running has stopped opponents with less than 200 yards total offense. Henning: "If the defense plays that well every week, we'll be in games no matter who's playing offense."

Nine of the 11 defensive starters are Beathard's draft choices, free agents and/or trades. The team that Allen built is forever gone, replaced by one with a championship of its own. Only hard-hearted souls would point out this was accomplished in a bastardized half-season, but even those hard hearts know that everyone played the same half-season--and no one, not even the Cowboys, played it as well as the Redskins.