After 14 weeks of injury and inconsistency, the most predictable thing of all has come to pass for the Washington Redskins.

They must defeat the Dallas Cowboys Sunday at Texas Stadium.

A victory in this game, which starts at 4 p.m. (WDVM-TV-9), would help the Redskins achieve Coach Joe Gibbs' team goal No. 1: making the playoffs.

"We know that if we lose this sucker," veteran running back Joe Washington said, "then we might as well put our season in mothballs."

For this game, the facts don't speak. They scream: the Redskins, Cowboys and New York Giants are tied for first place in the NFC Eastern Division at 9-5, with St. Louis a nudge behind at 8-6. Only two games remain in the regular season.

It seems that the playoff possibilities still are multiplying. But the Redskins know one thing: if they win their last two games (they play St. Louis next Sunday at RFK Stadium), they will make the playoffs.

If you can believe this, it's even possible the Redskins could play Dallas a third time this season, in a wild card playoff game.

It also is conceivable the Redskins could lose to Dallas, beat St. Louis and still make the playoffs.

Team owner Jack Kent Cooke said that running back John Riggins has told him he will play Sunday. Riggins has rushed for 1,052 yards this season and his presence seems imperative against the Cowboys, who have given up more than 200 yards rushing in four games this season, 203 in a 14-3 loss at Buffalo. Rush defense seems to be the Cowboys' window of vulnerability.

The Redskins' only uncertainty seems to be whether all-pro wide receiver Charlie Brown will play. He is suffering from what the team trainer, Bubba Tyer, calls a "mild sprain" of the left knee. Brown said after a short workout today that he won't know until pregame warmups whether he'll play.

In fact, there has been displeasure at Redskin Park this week over Brown's own uncertainty. Privately, members of the organization have said a "mild sprain" should not keep a player from competing in such a crucial game.

"It has to be a player's decision," Gibbs said. "As a coach, I don't know what the player is feeling. Players have to tell me. I think Charlie wants to play and will play, if he can."

Brown, who says he will continue his standard road game procedure of soaking the knee tonight in the Jacuzzi of the team's hotel, said, "(Teammates) know as well as I do that if I'm hurt and can't run, I would hurt the team by playing. If I can go, I'll go. I don't worry about what people say . . . Either way, I won't be able to run the way I want to."

Odds makers favor the Redskins by two points, perhaps a reflection of their 34-14 devastation of Dallas at RFK Stadium in October. This marks only the second time that the Cowboys have been underdogs at Texas Stadium, where they have played 111 times.

Most of the bravado this week has emanated from Dallas. Cowboys Coach Tom Landry says it will take 24 points to win this game. "I don't know why he says that, but then I've never been able to figure whether games will be 10-7 or 32-30," Gibbs said.

This is how the Dallas papers have quoted the Cowboys:

Reserve linebacker Jeff Rohrer: "I absolutely love being the underdog. We have been on top so long that now it's kind of neat that we can turn the tables a little bit. Now, we can stick it to them the way they stuck it to us."

Defensive tackle Randy White: "They're just a football team just like anybody else. They aren't superhuman by any stretch of the imagination . . . I think we can beat them. I won't make any bones about it."

Of course, Gibbs has read these quotes to his players in team meetings. In his role as master motivator, he also has told the players that the Dallas defense, led by all-pro White, has had 17 quarterback sacks in its last two victories, over New England and Philadelphia.

Deciphering Landry's offense has never been easy, Redskins coaches say. Defensive coordinator Larry Peccatiello, who figures he's prepared for games against Landry 15 times, said, "Landry's timing on when to go to play-action passes or when to slip in a gadget is better than any coach I've seen. Having him call plays is a real asset. Of course, the more you play against somebody, you develop a feeling on what he'll do. But that goes both ways. So from that standpoint, it's a push."

The Cowboys breathe a little easier now with the return of injured offensive linemen such as right guard Kurt Petersen and right tackle Phil Pozderac, both of whom are expected to start after recent absences. Petersen will have to cope with all-pro defensive tackle Dave Butz, who seems to save his best for Dallas.

The Redskins have kept Dallas Week verbal sniping to a minimum. "On the surface, there's not as much emotion as when we went down to play them in Dallas last year," strong safety Ken Coffey said, reflecting on the Redskins' 31-10 victory that guaranteed the home field advantage in the postseason.

"Last year, the Redskins were chasing the Cowboys for 13 or 14 weeks and we were always looking to that Dallas game. Whereas this year, it's really the Redskins, Cardinals, Giants and Dallas. So now, it's more like it's this game on top of everything else," Coffey said.