After eight struggling weeks, the Redskins found out yesterday how easy it can be to win.

All that's needed is a quarterback who is passing well, a kick returner who keeps threatening to score every time he touches the ball, a defense that makes four interceptions and an opponent that waits until the fourth quarter to play well.

"When things go right, it's not a hard game, really," quarterback Joe Theismann said after the Redskins overwhelmed the St. Louis Cardinals, 42-21, at RFK Stadium for their second straight victory and third in four games. "You'd really never know this was the same team that started off the season with five straight losses."

The Cardinals certainly must have thought the wrong opponent showed up. This surely didn't look like the same team they beat six weeks ago, 40-30, when the Redskins were victimized by turnovers, penalties and horrid special team play.

In scoring their highest point total since 1975, the Redskins were nearly perfect for three quarters. They took a 28-0 lead before St. Louis quarterback Jim Hart created some tense moments for the winners by passing for three touchdowns within an eight-minute span of the fourth period.

Washington finally ended Hart's comeback efforts on linebacker Monte Coleman's interception, the fourth for the Redskins, with three minutes left. Moments later, fullback John Riggins scored his third touchdown, on a four-yard run, to add to his team's 35-21 lead.

"I thought once we were up 28-0, it was a long way for them to come back," Coach Joe Gibbs said. "But I guess you never completely relax. Coaches like to punish themselves like that."

He probably should have relaxed after the game was 5 minutes old. It was apparent then that this was the Redskins' day.

On the game's third play, Theismann and receiver Art Monk teamed on a 38-yard touchdown pass after Mike Nelms returned the opening kickoff 46 yards to midfield. The score came on the pattern the Redskins had designated in their offensive plans as the one most likely to succeed against the Cardinals.

On the game's seventh play, free safety Mark Murphy intercepted a poorly thrown pass from Hart at the Redskin 36 as St. Louis tried to beat Washington deep, just as Miami and New England did the last two weeks.

On the game's 10th play, Theismann combined with with receiver Virgil Seay for a 51-yard scoring play: Redskins 14, St. Louis 0. The Cardinals never recovered.

Ever since Gibbs decided four weeks ago to abandon a wide-open passing offense and stick with a more basic two-tight-end approach, the Redskins have shown weekly improvement. They cut down drastically on their their turnovers and penalties, they discovered a running game and, now, the last piece of their offensive puzzle -- those long-gaining plays -- finally has fallen into place, at least for one afternoon.

Add the interceptions, including two by rookie linebacker Mel Kaufman, plus a decent pass rush on Hart and outstanding coverage for three quarters by the Redskin secondary, and no wonder Gibbs was moved to call this "by far our best game of the season."

The victory also showed how effective the Redskins can be when most of their best players are healthy. It's no coincidence that the Redskins have improved since Nelms, Riggins and Washington, all of whom missed the first St. Louis game, have returned from injuries.

Besides the opening return, Nelms had a 40-yard punt return down the right sidelines that included a five-yard, stumble-and-try-to-keep-my-balance ending through three would-be tacklers. In the fourth period, after St. Louis has scored its first touchdown, he took a kickoff straight up the middle, leaped like a high hurdler over a Cardinal at midfield and was finally downed at the seven after an 84-yard return.

Riggins, despite his standing as the ninth all-time rusher in NFL history, never had run for three touchdowns in a game. He achieved that mark yesterday on rushes from the one, one and four as the Redskins were able to score from in close, something they weren't able to do earlier in the season.

Joe Washington had his best day rushing as a Redskin (93 yards on 23 carries), and caught four passes for 22 yards. His sweeps around either end never allowed the Cardinals to focus completely on stopping Theismann.

Theismann was the one Redskin St. Louis needed to stop. "Could have threaded a needle with a football," he said about his 14-for-19, 219-yard, no-interception day that included completions on eight of his first nine attempts.

Theismann, who has not thrown an interception in two weeks, credits much of his recent success to a healthier right thumb. "I hurt it pretty good against Dallas (in the opener)," he said, "and I wasn't able to grip the ball as tightly as I need to. Now I can. The last few weeks, everything feels great."

Of course, completing a couple of quick touchdown passes would make any quarterback feel good. The first one, to Monk, was set up when the Redskins noticed during the week that the Cardinal strong safety, Lee Nelson, sometimes plays very close to the line.

"He plays lots of little games at the line," said Monk, who later had a leaping 10-yard touchdown catch. "We caught them when he was up close, so I was on my guy (Carl Allen) alone. I ran a post and got by him and the pass was right there."

Seay also picked on Allen for his touchdown. The play was designed as a simple five-yard hitch, but Seay, a 5-foot-7 first-year man who has been starting for two weeks, turned in into a long touchdown by getting through pressure at the line.

St. Louis immediately drove to the Redskin one, but an illegal motion penalty cost the Cardinals five yards. On second down from the six, Hart was forced to his right. He tried to throw back to his left, into the end zone. Kaufman, starting for injured Brad Dusek, was playing his zone assignment and easily picked off the poorly thrown pass.

The Redskins turned that break into a 80-yard, 12-play touchdown drive ending in Riggins' first one-yard run. Three completions by Theismann and a pass interference call on Allen preceded the score.

After Theismann's fumble at the Cardinal 10 (the Redskins' only turnover) in the third stopped another threat, Washington extended the lead to 28-0 on Riggins' second one-yarder. Kaufman's interception off a tipped pass by cornerback Joe Lavender started the drive at the Redskin 46.

But not even Hart, who finished with 305 yards by completing 24 of 39 passes, could overcome an initial 28-point deficit.

Gibbs could be especially happy about the victory since it appeared his team got through it without any major injuries, a first this season.

"All you had to do was show the films of the last game (with St. Louis) to get a team ready for this one," Gibbs said. "They whipped us badly, they whipped us physically the first game, and you don't want that to happen again.

"We're playing sounder football now. And now we feel we can win. Against anyone we play."