In a season of big hits by the Redskin defense, none is likely to be remembered more than Dexter Manley's crushing blow on quarterback Danny White in the NFC title game.

Everything the defense has stood for this season--aggressiveness, hard contact and clean but physical play--is in that tackle.

White suffered a concussion, but that is not why it was noteworthy. What is significant is that the Redskins hardly hit anyone with authority last season.

But this season, that defense is one of the NFL's best, good enough to be No. 1 in fewest points allowed and good enough to hold its last four opponents to less than 100 rushing yards. The Redskins finished the regular schedule ranked fourth overall in the league, but in the playoffs there has been no better defensive unit.

The change from last season to this has been especially noticeable in Manley. A raw rookie last season who had quickness but little else, he has become a competent, sometimes spectacular player this year.

Last season, Manley was embarrassed in a December game at Dallas, when the Cowboys trapped and sucker-blocked him all day. His only response was a straight-ahead pass rush against tackle Pat Donovan.

But Manley got to White with a much more sophisticated move. He faked going outside, then cut inside Donovan and broke up the middle before his opponent could recover. He went straight for White, never leaving his feet, never making himself susceptible to a fake. He hit White in full stride.

"We never are out to hurt anyone," safety Tony Peters said. "We are all professionals trying to make a living. But it's important for a defense to hit hard and be aggressive. It's the only way to make things happen."

The defense began changing in training camp, first through the urging of its coaches. Then players like Peters, upset with his passive 1981 play, increased practice intensity.

"You see one guy do it and then you get inspired," said cornerback Vernon Dean.

Gradually, the players found that by charging after an offense, they were taking commmand of the line of scrimmage and the secondary. Receivers began dropping passes in the open field, especially coming across the middle. They said it wasn't intimidation. Cornerback Jeris White just smiled.

"You have to believe that when a guy gets hit once, he remembers it next time and it affects him," White said. "I think that is intimidation."

Run up the middle? Massive Dave Butz is waiting. Get by Butz and middle linebacker Neal Olkewicz, who made the team as a free agent rookie mostly because of his tackling, is next. Run outside? Linebacker Rich Milot has learned to use his 235 pounds as a force against the run. Go into the secondary? Take your choice: Peters, Dean and White thrive on body blows, and Mark Murphy, once asked to hang back and be a safety valve, now matches his mates hit for hit.

"You don't play defense without tough people," said Richie Petitbon, the defensive coordinator. "But people also don't realize that before you can be aggressive, you have to have experience and coordination within the whole unit. Our young players have grown up and we haven't had injuries. Everything has stemmed from those two facts."

Manley and fellow end Mat Mendenhall were first-year starters last season; now they are comfortable and confident. Linebacker Mel Kaufman was a free agent rookie who played only because Milot and Monte Coleman kept getting hurt; now he is good enough to make a key interception against Dallas. Cornerbacks Joe Lavender and Lemar Parrish, both in their 30s, were coverage men first and tacklers second; White and Dean are just the opposite, although Dean has covered marvelously the last month.

"You never can expect a dramatic difference from year to year," Petitbon said, "but you can hope for it. And what I like about this defense is that it's young enough to get even better."