When the RFK Stadium faithful realized Redskins finally had beaten Cincinnati, 28-14, yesterday, when they realized the NFL East championship would come down once again to the Cowboys and Washington, they began a chant that grew louder and louder as the clock ran down.

"Beat Dallas," they yelled. "Beat Dallas."

And that is what the Redskins must do next Sunday at Dallas to win the NFC East and finish off what has been a remarkable regular season for a team that was supposed to go home when the playoffs started this year.

By winning game No. 10 yesterday, Washington moved into a three-way tie with the Cowboys and Eagles for the NFC East lead. All have 10-5 records, but only Dallas and Philadelphia are now guaranteed playoff spots.

The Redskins still can miss a playoff berth, but it would take a loss to Dallas and a win by Chicago (9-6 over St. Louis to jeopardize their hopes. Then the tie with the Bears would be broken on the basis of most net points scored this season. Washington has a 33-point lead over Chicago in that category.

Also, it should be noted, the Redskins can qualify as the wild card team if Tampa Bay loses to Kansas City Sunday and the Bears down the Cardinals to win the Central Division race. The Bucs would have one more loss than the Redskins and would not qualify as a wild card entry.

But only Dallas was on the Redskins' minds yesterday. "A week is not a very long time to wait," quarterback Joe Theismann said of the Cowboy game. "Not when you are looking at a dream."

Theismann and teammates Clarence Harmon, Coy Bacon and John Riggins helped set up this dream game at Dallas. They performed outstandingly against the Bengals, who belied their 3-12 record by putting up a fierce struggle that wasn't finally decided until the final 46 seconds.

That's when Riggins, who had 95 yards for the day, scored his second touchdown on a two-yard run. One play before, he had turned a routine off-tackle slant into a 19-yard gain that put him over 1,000 yards for the second straight season and for the third time in his nine-year career.

Theismann, who plays better every week, saw two interceptions mar an otherwise splendid day. He had his second-best day as a pro, completing 23 of 34 passes for 296 yards and two touchdowns. He completed 23 passes, a personal high and his season total hit 2,597 yards, another individual high and tops for a Redskin quarterback this decade.

Harmon, the club's big-play utility man, performed his usual magic by turning two Theismann passes into touchdowns on the strength of sensational runs after the catches.

Bacon, the 36-year young "old man" of the Redskins, keyed a fine second-half effort by the defense with 3 1/2 sacks of quarterback Ken Anderson, a former teammate.

The game began as if each team would score 50 points. It ended with Washington holding the potent Cincinnati offense to its third lowest point total of the season.

"We did what we had to do," Bacon said. "Now it's Dallas. There is no reason we shouldn't play well. We're young and healthy Who's going to win? Whoever wants it the baddest."

For a while yesterday, the Redskins didn't seem to want to beat Cincinnati badly enough. The first two times the Bengals touched the ball, Anderson drove them to touchdowns and a 14-7 lead.

But Theismann rallied the Redskins with those two scoring throws to Harmon, the last coming with 50 seconds left in the half. Then three fine defensive plays by Washington in the second half kept the Bengals from coming back.

The first came on Cincinnati's opening possession of the third quarter. On a third down from the Washington 27, Bacon cleanly whipped tackle Mike Wilson and dumped Anderson for a 10-yard loss, forcing a punt.

The second came midway in the fourth, with the Bengals at the Redskin 10. On a third and one, rookie Charles Alexander swept to the right. But Tony Peters and Monte Coleman stopped him for no gain.

The Bengals, trailing 21-7, decided to go on fourth down. "I never hesitated," Cincinnati Coach Homer Rice said, "because we've converted over 80 percent of the short-yard plays all year. I thought with our line and with Pete Johnson, we'd pick up the yardage."

But Cincinnati needed a full yard to maintain possession and Redskin defensive end Perry Brooks, playing for Bacon, said, "We were able to call a defense that lets the linemen stand up more rather than getting low to the ground, like we must on fourth-and-inches."

So Brooks had a good view of the 260-pound Johnson taking the ball from Anderson and trying to cut over left tackle. Brooks penetrated and slammed into Johnson, holding on until help came from Coleman, Neal Olkewicz and other friends.

"When we didn't gain anything on that play," Rice said, "that was the turning point of the game."

Cincinnati made it easier for Washington in the second half by foregoing running plays and concentrating mainly on passes. Anderson tossed 21 passes after intermission, mostly into the Redskin nickel defense during the fourth period.

"We didn't want to give up a bomb to Isaac Curtis," Coach Jack Pardee said. "We went to the nickel so much hoping we'd hold up on the run and we did. When they didn't run, our pass rush picked up. But to win, we couldn't give up bombs, at least not too many."

The only long play Washington did surrender was a 52-yard pass from Anderson to Archie Griffin with 2:30 gone in the game. But it was a busted play, with Griffin sneaking out of the backfield, catching a short toss from the scrambling Anderson and outrunning his pursuers into the end zone.

"We must be in the top percentage, holding them to 14 points," Pardee said, "but the way it began, I thought we wouldn't hold them to 40."

Washington probably should have scored more than 28 points. But those two Theismann interceptions botched fine opportunities, although the two drives fulfilled the Redskin goal: they kept Anderson and Co. off the field for long periods of time.

Following the Griffin touchdown, Washington quickly tied the game. Theismann got things rolling on a two-yard toss to Danny Buggs on what was supposed to be a screen play.

But when the Bengals pressed Buggs at the line of scrimmage, the wide receiver took off down the sidelines and Theismann led him perfectly over the shoulder of cornerback Ken Reilly.

"Danny read it the same as me," Theismann said. "He's supposed to take off like that."

An eight-yard sweep by Benny Malone and a two-yard gain by Riggins brought up a fourth down at the Bengal seven. Pardee thought his team had a yard to go, so he sent in the field goal unit. But a measurement showed the distance to be only inches, so he went for a first down. Theismann had requested the measurement to give Pardee extra time to make his decision.

Riggins responded by heading off right tackle, breaking one hit and romping into the end zone for the score.

Again, Cincinnati drove for a touchdown, this time on a 76-yard march that ended in a one-yard plunge by Johnson. It took the Redskins until the middle of the second quarter to retaliate.

This show belonged to Theismann. On a third and 13 from the 50, he unloaded a soft pass just as the Bengal front line was swarming him. The ball wound up on Ike Forte's fingertips at the 35 and he raced to the 23 before being tackled.

Then, after Buggs had grabbed a 17-yard pass for a first-down at the six, Theismann shook off a one-yard loss by rolling to his right and trying to direct Buggs into the open.

"I wanted to go to Ike or Clarence but I saw Danny coming open. Then he got knocked over. So I looked over the mountain (of Bengal rushers) and, lo and behold, there was Clarence. I threw it low and he caught it."

Harmon said once he saw Theismann in trouble, "I realized the play was botched, so I turned inside and Joe saw me. Then I tried to get in."

Theismann unleashed the ball despite being hit by three Bengals. Harmon grabbed it on the two and slammed in the end zone. Mark Moseley added the extra point for a 14-14 tie.

The Bengals moved the ensuing kickoff to the Washington 41, where Rice tried for a first down on fourth and one. But Olkewicz and Dusek stopped Johnson's up-the-middle try and the Redskins took over with 2:15 to go.

"We ran just another simple two-minute drill," Harmon said. Theismann, a master of those drills, completed passes of 12 yards to Don Warren, eight to Forte, two to Buggs and 11 to Forte to set up a first and 10 at the Bengal 23.

Harmon ran "a seven-yard pattern" hooking over the middle. There was no Bengal in sight when he took Theismann's pass. At the five, Harmon twisted away from Marvin Cobb, at the three he ran over Dick Jauron and finally fell into the end zone.

Another Moseley conversion and Washington was in the lead for good, 21-14, with 42 seconds to go in the half.

Washington's major threat after intermission came after a Bengal punt died on the Redskin one. Despite two penalties, the Redskins moved to the Bengal 25 thanks mainly to a 25-yard pass to John McDaniel and a reverse-the-field run by Forte.

On third down, after another holding call, Theismann tossed a high pass to Ricky Thompson and Scott Perry intercepted. Washington had run 16 plays and gone 74 yards in 8 1/2 minutes, only to come up empty.

Cincinnati could never capitalize on that break and Washington, needing to gain net points on the Bears, finally scored again after the Bengals failed on a fourth down at their 19.

Theismann had already decided to kill the clock with 55 seconds left. But McDaniel carried a message in from the sidelines: "Give the ball to Riggins and then we'll kick a field goal."

But Riggins, taking advantage of Cincinnati having only 10 men on the field, sprinted to the two to go over 1,000 before going into the end zone on the next down.