IT IS TIME now, for the post-mortems on the Redskins' season of 1977 and the operative, indispensable word, without it is impossible to be a serious analyst, is if . For example, some will tell you that if mark Moseley had not missed three field goals in the second Dallas game (always assuming the rest of the game had proceeded exactly as it did proceed, which is a dubious assumption) the Redskins would have needed help from nobody to get into the playoffs as a wild-card team. Those who so speculate, however, usually neglect to ask what would have happened if Mr. Moseley, a gifted and usually reliable fellow, had not successfully kicked four field goals against the St. Louis Cardinals two weeks ago; on the same assumption the season would have been over and Sunday after noon would have been, well, just another Sunday afternoon, instead of an aging experience for serious Redskins followers. You can as persuasively boil down a whole season to the fingertips of Ed Marshall of the new York Giants; if he had caught a perfect pass that he dropped in the snow on Sunday against the Bears, or dropped a flukey pass that was tipped into his hands on a deflection by Ken Houston in the redskins opener against New York . . . what then? You can also put it down to an extraordinary run of penalties - or, if you prefer, injuries. If Chris Hanburger, and Pat Fischer and John Riggins and Mike Thomas and assorted other heroes had not been disabled or slowed down . . . who knows?

Who, indeed? The point, or perhaps the pointlessness, of this exercise was nicely underscored by our favorite post-mortem if . Even before the Redskins had been finally eliminated in the gloom of evening on Sunday, Coach Allen was arguing that if only a differnt method were used to calculate point differentials between teams with identical records, the Redskins would almost certainly not have needed help from the Giants to win the wild card. The coach is absolutely right. But the thing is that a different method isn't used. So what the Redskins needed was to have scored more points during the course of the year - particularly more touchdowns. It would also have helped to have won more games.

That pretty much winds up our post-mortem for the 1977 Redskins. If the season had its ragged beginnings, our instant replay is crowded with bright moments, as well. If there are to be no playoffs for the Redskins well, they at least kept the question excruciatingly open, in their own, familiar, heart-stopping way, right up to the end. Next year will be different - you can, as they say, depend on it. In the meantime . . . dream on.