Doomsday in Dallas came last January, when a leaping catch by San Francisco receiver Dwight Clark denied the Cowboys another trip to the Super Bowl and gave Coach Tom Landry an offseason to brood about "one of my toughest losses."

That's not good news for the rest of the NFC East, because an agitated Landry usually produces his strongest teams. And the Cowboys at their best are the NFC's best Super Bowl possibility, with apologies to the 49ers.

The Cowboys' major concern is a defense weakened by the retirements of linebacker D.D. Lewis and safety Charlie Waters. Lewis will be easier to replace than Waters, who held together the secondary last season. But with the continued improvement of quarterback Danny White, the development of halfback Tony Dorsett and the revitalization of receiver Tony Hill, Dallas' offense could be so strong that defensive breakdowns hardly will matter.

Even though quarterback Phil Simms is sidelined with a knee injury, the New York Giants still have the talent to move ahead of Philadelphia as the division's second-best team. But they won't unless quarterback Scott Brunner equals his season-ending 1981 performance, when he helped drag the Giants into the playoffs.

Another problem, the contract holdout of halfback Rob Carpenter, is out of Brunner's control. Carpenter, the team's only good running back, would be sorely missed. His absence could reduce the Giant offense to its former punchless days.

There is plenty of defensive punch, especially at linebacker, where Lawrence Taylor became an instant terror last season. Still, only more offense will prolong the Giants' improvement.

It will take more than another tough training camp to improve Philadelphia, which slumped badly last November and now has lost nose guard Charlie Johnson. More speed at receiver, possibly supplied by rookie Mike Quick (North Carolina State), and the return of quarterback coach Sid Gillman could help Ron Jaworski. But there is no ready solution to protecting overused Wilbert Montgomery. If he gets hurt, watch how fast the Eagles tumble, even with one of the NFL's most efficient defenses.

On their way down, the Eagles could pass the rising Redskins, whose youth program may nudge them out of their pattern of mediocrity (24-24 the last three years). Washington has to improve or risk being passed by the intriguing Cardinals, who somehow continue to upgrade themselves despite organizational disorganization.

St. Louis is committed now to young quarterback Neil Lomax, with Jim Hart serving as a backup and tutor. And tackle Dan Dierdorf now is a center and receiver Mel Gray is a second-stringer. This, too, is a team dependent on young players with impressive college records. This year will show how quickly they can learn.