It might seem a bit early to be attaching significance to the National Football League's division races, yet Washington-area fans will be looking for signs that the St. Louis Cardinals' decline is serious.

If the unbeaten Dallas Cowboys win today in St. Louis(4 p.m. WMAR TV-2) they will have a three-game lead over the team that has won the NFC East title in two of the last four years. The Cowboys are 51/2-point favorites.

The Redskins go to Dallas next Sunday, and if they can't stop the Cowboys, the notion may begin to develop that Washington's best playoff hope will be as a wild-card team.

The Cowboys have scored 80 points, second in the league to New Orleans, which fattened up on Chicago, 42-24, to raise its total points to 81.

Once reputed as the big-play Cardinals, they are 1-2, and are guilty of a back-slide on offense, averaging 10 points in three games.

The Cardinals led the NFC in total offense in 1976; now they are fourth. They were sixth in total defense last year; now they are eighth.

The Cowboys were second in offense in 1976; now they lead. They were fifth in defense last year; now they are third, with unusual depth in fast, young linebackers.

Roger Staubach ranks as the No. 2 passer in the NFC behind Greg Landry of Detroit, but he is the leader in two important categories, with a 61.4 completion percentage and 7.75-yard average gain per pass.

In Baltimore there will be a battle for first place in the AFC East between two unbeaten teams, the Colts and the surprising Miami Dolphins. New England, a preseason pick to be in contention because of having the easiest schedule in the league, is 1-2 and plays the 2-1 Seattle Seahawks in Foxboro, Mass.

Two division leaders play in Cleveland, the 2-1 Browns of the AFC Central and the unbeaten Super Bowl champion Oakland Raiders.

In the NFC Central, the Detroit Lions play the Vikings in Bloomington, Minn., for the lead, each having 2-1 records.

The Monday night game is another big one, with the 2-1 Los Angeles Rams opposing the 1-2 Bears in Chicago.

The remainder of the schedule pits the Kansas City Chiefs (0-3) against the Broncos (3-0) at Denver: the New York Jets (1-2) against the Bills (0-3) at Buffalo; the Pittsburgh Steelers (2-1) against the Oilers (2-1) at Houston; the Atlanta Falcons (2-1) against the 49ers (0-3) at San Francisco; the Philadelphia Eagles (1-2) against the Giants (1-2) at East Rutherford, N.J.; the Redskins (2-1) against the Buccaneers (0-3) at Tampa Bay; the Cincinnati Bengals (1-2) against Green Bay Packers (1-2) at Milwaukee, and the San Diego Chargers (2-1) against the Saints (1-2) in New Orleans.