Rhythm, Joe Walton keeps preaching to Joe Theismann. Rhythm and timing. A quarterback with an accurate fast ball can live comfortably for years in the NFL if he chisels that notion in his mind.

"You do that and it's darn hard for anyone to intercept you," the Redskins' offensive coordinator said. "Also, it's darn hard for anyone to get any sacks. Joe just believes now. And this was the best he's done."

The Jets helped Theismann during his 21-for-30 afternoon yesterday in RFK Stadium. Their cornerbacks started each play closer to Alexandria than to Redskin receivers, so Theismann had sideline passes up to 12 yards anytime he chose. Obsessed with stopping the Redskin bombs, the Jets were shot down with grenades.

Theismann is emerging as the quarterback of his considerable dreams, poised now and always confident, willing to concede that not every pass can be completed and grateful the Redskins - at last - have an offense with some imagination.

"Joe Walton is the greatest thing to happen to men in football," he said. "The biggest change for me on the field is an awareness of where everyone is. But the steps, threes, fives, sevens, are coming along. Throwing to the left still feels kinda funny. Throwing to the right feels just right.

Those numbers are the steps Theismann takes backward before he releases a pass. Yesterday, he was taking five-step drops most of the game - and getting the pass off less than 1.5 seconds after taking the snap.

"If you get passes off that quickly," Walton said, "they'll be good. I don't care how good the cornerbacks are."

And when the cornerbacks are beaten often enough a John Riggins can run far enough to gain the yards necessary to make the history books. Riggins 114 yards rushing yesterday lifted him over 5,000 for his NFL career. Like Theismann, he is a late Redskin bloomer.

"These past two haven't been bumper crops," he admitted, "so I hadn't been thinking about anything like that. By the way, how many other runners have 5,000?"

Twenty-five.

"Well then, it doesn't mean all that match. When I started my career (with the Jets eight years ago), I wanted a shot at 12,000. Only one man (Jim Brown) ever did that. If it takes me eight years to do it, I ought to be in the Hall of Fame for longevity."

By midway through the third quarter, it was becoming clear that the Redskins could hold everyone but the cheerleaders - now rated G - and still win. On an 11-penalty day, they still won big. And Theismann could glimpse eight days into the future.

"When the Jets were giving us that four-line-man rush, I had to admit I was thinking about how that would help us against Dallas," he said.

"We really haven't seen the 4-3 that much, so every little bit helped us prepare for the Cowboys."

What the Redskin fans and coaches appreciated most from Theismann yesterday, even beyond his discipline, were on-target passes during difficult patterns. Twice he threw long sideline completions that had to be soft enough to clear a line-backer and hard enough to beat the cornerback.

"But did you see my blocking?" He said.

Yes.That came during the drive that lifted the lead to 20-3 in the third quarter, on a Mike Thomas-to-John McDaniel reverse. Theismann put a more than passable block on Bobby Jackson, put him on the ground in fact, and McDaniel gained 12 yards.

For those who consider him something less than a complete quarterback, because Walton sends in all the plays, Theismann counters that he changes the call at the line of scrimmage now and then and then offers a look that says: "So what?"

All help is gratefully accepted.

And those od times Theismann calls time are because either the coaches suggest something that patently will not work or the messengers have garbled the message.

"For instance, we have a play called 'slot 37 bob," he said. "Well, somebody might come in and tell me to run 'Slant bob.' That can be run both ways. And I knew that one reverse (that ended as a sizable loss) wouldn't work when we lined up. I should have changed it at the line.I didn't."

Walton and Theismann both agree that the offensive success in the season's fourth game was partly because of what worked so well in two of the three earlier games. Success breeds confidence, which breeds more success.

All of a sudden Redskin faithful who would happily have settled for a 3-1 record before the Cowboy game are dazzled by 4-0. All of a sudden a game that once was regarded with rampant pessimism seems most intriguing.