In the good old days, before instant replay officials, coaches used to say that when you passed the football, three things can happen and two are bad: an interception or incompletion.

The Redskins defense must make this football adage come true today at RFK Stadium against Atlanta if they are to advance to the NFC championship game next week.

The Atlanta Falcons will complete 50 percent of their passes. If the Redskins are to win, Atlanta's receivers must drop some passes, Redskins defenders must knock down some others, and most important, the Redskins must make some interceptions.

Atlanta's "Red Gun" offense has the potential to inflict some pain, but not a lethal knockout punch. Little-known 5-foot-9 rookie Erric Pegram will be Atlanta's featured running back since Mike Rozier and Steve Broussard are fighting injuries.

Pegram has carried the ball for 349 yards this season, and will run two plays: the draw and the counteraction pick-a-hole.Pegram has not shown he can be a 100-yard a game back, which is what the Falcons need to win.

But Falcons Coach Jerry Glanville recognizes the inherent weakness of his "Red Gun" offense by his own admission: He runs the ball just for show, not with the expectation of any real success. The "Red Gun" is a possession-type passing attack that has been effective the last four weeks as a substitute for the running game.

One "Red Gun" formation has two wideouts on each side of the field, and with motion on occasion, works into a three-wideout position. Atlanta has three fine receivers -- Andre Rison (81 receptions), Michael Haynes (50) and Mike Pritchard (50).

All three are capable of running well with the football after they catch short passes. This, in reality, is the Atlanta running game.

The Falcons use combinations of one receiver clearing out with the second receiver running a short out, or hitch, pattern. In addition, they are running screens with the same action, with their two guards pulling in front of the receivers instead of the normal set-up in front of the running backs.

These patterns are effective against either a zone or a man-to-man defense. With the man defense, you have a good pick play, and with the zone defense, it's difficult to tell a cornerback to jump on the short patterns. The cornerback should not react to the short patterns immediately. If he does, Atlanta will send the second man through the zone, going deep, catching either the linebacker or cornerback off guard.

Every zone defense eventually turns into a man-to-man because defensive backs have to get next to the receiver catching the ball. The safeties must be as deep as the deepest man and in a position to get as wide as the widest man when the ball is thrown in their zone. They must react to both the man and the ball.

The rules for this game are simple and fundamental: Redskins safeties Brad Edwards and Danny Copeland must make good decisions with the angles they take to get to the ball, and they must run through the receivers when they get to the collision point. Haynes, with his world-class 4.3 speed, will go deep frequently. If the Redskins' safeties don't follow this rule, Washington could lose.

The Atlanta defense uses seven men on the line of scrimmage on almost every play. This commitment to stop the run on first and second down puts extraordinary pressure on its defensive backs. The Redskins know the Falcons are vulnerable because of their single coverage with Tim McKyer and Deion Sanders. These are fine cornerbacks, but are not capable of covering The Posse man-to-man.

The predictability of Atlanta's pass defense and Washington's ability to pick up the blitz, giving Mark Rypien time to look downfield, should lead to a Redskins victory today.

Pat Fischer, 51, played in the NFL for 17 years, including 10 (1968-77) with the Redskins. He was considered one of the toughest cornerbacks to play the game.