"Three-and-oh, thrice-and-oh," the Redskins chanted in unison yesterday as they left the field after a stuningly simple 28-10 mastery of the bumbling St. Louis Cardinals. "How good are we?" Mike Thomas asked. "Hey baby, we've got something going here."

What the Redskins had going best for them yesterday was another dazzling performance from rookie return man Tony Green, who ran 99 yards with a kickoff for the first Washington touchdown and set up the second with a 27-yard punt return that almost went all the way too.

Green suffered what team physician Stanford Lavine described as sprained ligaments in his left knee on that first-quarter punt return when he was stopped by Lee Nelson, the last Cardinal in his way to the end zone.

Lavine said it was to early to evualuate the severity of the sprain. Coach Jack Pardee indicated shortly after the game that it did not appear serious and ventured that Green probably would recover in time to play Sunday in RFK Stadium against the New York Jets.

The Redskins were beating the Cardinals for the fifth straight time over the last three years, and more important, propelling teamselves into first place alone in the NFC East with the Los Angeles Rams' defeat of the Dallas Cowboys. The Redskins play the Cowboys on Monday night football in two weeks at RFK.

Green provided the most spectacular plays of the game while fullback John Riggins made yardage the hard way. Riggins lugged the football 16 times for 108 yards - a 6.8 yard rushing game since the 1976 season.

Dispite suffering all day from heat cramps, tailback Thomas skittered 78 yards in 16 carries, including a nine-yard touchdown run, while Clarence Harmon contributed 50 ground yards and caught a nine-yard touchdown pass from quarterback Joe Theisman.

In all, the Redskins galloped for 255 yards rushing against a Cardinal team ranked 14th among 14 National Conference teams in defense against the run. Washington had not gained that many yards on the ground since 1976 either.

Theismann threw the football a mere dozen times, completing five for 59 yards including a 14-yard touchdown pass to tight end Jean Fugett 88 seconds into the second quarter.

After Theismann connected with Harmon for a touchdown with 4:35 left in the third period, Pardee felt comfortable enough about a 23-3 lead to allow Billy Kilmer to work off a bit of rust and finish out the game. It was erstwhile regular quarterback Kilmer's first regular-season action.

"I felt like we were in pretty good control," Pardee said. "He (Kilmer) hadn't played in several weeks. He's got to be ready to go full tilt at any time. I just felt it was a good time for him to get some work."

Kilmer dressed quickly after the game and when a reporter asked if it bothered him to be used in a mop-up role he said tersely, "Whatever Jack wants to do." Then he hurried out the door.

The winless Cardinals never were in the game after running back Steve Jones dropped what should have been a two-yard touchdown pass from quarterback Jim Hart on St. Louis' second series. Instead, the Cardinals had to settle for Jim Bakken's 20-yard field goal. Then Tony Green took over.

Green fielded Steve Little's kickoff at his one-yard line and immediately veered to his right. Blocks by Harmon and Karl Lorch got the Florida find into daylight at his 30. He cut back to his left at the -10 and was long gone. Green even slowed down at the Cardinal 30 and no St. Louis defender was within 20 yards of him when he spiked the football behind his head with 4:57 left in the first period.

"The thing people don't realize about Tony is that he's got great strength in his thighs," said special-teamer Pete Wysocki, who also threw a crunching block on the return. "That gives him the ability to move sideways real well, and he freezes people with his moves.

"With Tony running, you don't even have to destroy your man. All you need is to nick him, just get a little piece. Tony sees the crack and he jets in. And that play really hurt St. Louis. Those plays destroy morale - quickly.

Green helped make it worse for the Cardinals the next time he touchdown the ball. This time he fielded Little's punt at the Washington 21 and whoosed right up the middle before Nelson came flying into his knee and sent him down and out for the duration of the game. But with that 27-yard return, more damage had been done to the Cards.

Starting off at their 48, the Redskins moved steadily up the field. Not even a holding call on guard Dan Nugent deterred their progress, because tight end Reggie Haynes picked up 13 yards on a razzle-dazzle reverse and Theismann hit Frank Grant with a key seven-yard pass at the sideline on third and two.

Two plays later, on first and 10 at the 14, Theismann dropped back to pass and managed to get the ball off just before linebacker Steve Neils smacked him to the ground. Theismann later described the pass as "a side-winding floater, kind of ugly, really."

Nevertheless, Fugett was all alone at the two-yard line to haul it in and hotfoot it into the end zone for a 14-3 lead with 13:32 left in the half.

"It was just a crossing patter," Fugett said. "I lined up on the left and our two receivers were on the other side. We just crossed and it's a tough play to defense. I don't know what happened to the guy who was on me. Maybe he got picked off or he slipped. I don't worry about those things. Let them worry."

The Cardinals were doing plenty of worrying midway through that second period when the Redskins took over at midfield again and drove 50 yards in five plays - including Riggins 26-yard burst around left end - before Thomas scooted through the middle for nine yards and a 21-3 lead.

The crowd of 49,282 booed, and when team owner Bill Bidwill appeared on the field at halftime in a ceremony to honor Cardinal hall-of-famer Larry Wilson, the stadium rumbled with the sound of unhappy customers.

Cardinal fans blame Bidwill for the collapse of the team, particularly the loss of game-breaker Terry Metcalf to Toronto. But what could the Cardinal owner do about the eight passes dropped by Cardinal backs and receivers yesterday?

Nor was there anything Bidwill could do about a Redskin defense that held quarterback Jim Hart to 16 completions in 40 passes, with one interception and two sacks. The Cardinals gained 328 yards of offense, but mostly too little, too late.

The Redskins put the game away for good with the sort of touchdowns drive Pardee, as all pro coaches, loves to see. It covered 86 yards in 13 plays and ate almost five minutes off the clock, a major factor against a Cardinal offense still suspected of having big-play capabilities.

Riggins gained 31 yards rushing in five carries on that drive, and on one play pitched the football back to Theismann in a repeat of last week's flea-flicker play that turned into a toudhdown bomb and helped defeat Philadelphia.

This time the opposition was prepared and Theismann was forced to scramble for a one-yard gain. Never mind Theismann kept the drive alive with passes of 16 yards to Harmon and 13 to Riggins in third-down situations.

That pass to Riggins carried to the Cardinal nine, and two plays later Harmon came out of the backfield, ran a basic post pattern and caught the ball in the end zone with safety Ken Greene on his back for the touchdown and, with Mark Moseley's fourth conversion, a 28-2 lead.

The Cardinals of 62-year-old rookie pro coach Bud Wilkinson finally scored a touchdown with a bit of razmatazz of their own early in the fourth quarter. On first down at the Washington 27. Jim Otis took a handoff and veered toward his left end.

Redskin defensive end Coy Bacon had a grip on Otis from behind, but the Cardinal fullback flipped a lateral to swift Mel Gray. A sideline stande throughout the first half because of a hamstring problem, wide receiver Gray demonstrated precisely why he was pressed into desperation service after intermission.

He zoomed around his right end and down the right sideline. Redskin safety Ken Houston got to Gray near the goal line, but the ensuing crash into a teammate propelled Gray across.

Roger Wehrli recovered an onside kick for St. Louis on the ensuing kickoff, but his team failed to get a first down on its next series, or any series thereafter.

So the Redskins rolled on, even as Pardee kept insisting, "I really don't know how good we are."

"I just know I feel great, the whole team feels great," said Thomas.

"Everybody is hustling, everybody is working hard and contributing, and we're starting to work for each other. I think we'll have a great football team. We're fighting together, and we just keep getting better every week."