With their usually efficient offense throttled by rain and a tenacious Philadelphia defense, the undefeated but always threatened Redskins found they also could play defense yesterday, beating the Eagles, 13-9, on the strength of two fourth-quarter interceptions.

Despite a persistent rain and chill, a crowd of 48,313 showed up (6,732 passed up the opportunity) at RFK Stadium to watch Washington play its first home game of the season and first in 350 days. The fans came away cheering the Redskins' fourth straight victory and some new heroes: defensive backs Jeris White, Tony Peters and Mark Murphy.

It was White who intercepted two of Ron Jaworski's passes in the first half to help Washington to a 10-0 lead that should have been at least a touchdown larger. It was Murphy who picked off a pass midway through the fourth period with the Eagles at the Redskins' 15. And it was Peters who preserved the victory with an interception at the Washington nine with 103 seconds left.

Now the Redskins, who with the Miami Dolphins are the only unbeaten teams in the NFL, await 3-1 Dallas Sunday at RFK. "A big day for this team," Coach Joe Gibbs said of the game with the Cowboys. Washington's victory yesterday was the first of this strike-shortened season in which its offense did not dominate.

"This game belonged to the defense," said Gibbs, whose team has won seven in a row over two seasons and 12 of its last 15, including six straight in RFK.

"I hope this is the game that will really make our defense . . . Our offense has played well until now, but today, we just weren't working smoothly. We took our best shots, we tried everything in the book, but 13 points was the best we could do."

Thirteen points was enough, but just barely, against a Philadelphia team that desperately fought to avoid its third loss in four games. Just two years after making the Super Bowl, the Eagles will have to scramble to make the playoffs, mainly because they committed five turnovers, two more than the Redskins.

Quarterback Joe Theismann and his offensive mates had their moments. Theismann threw a 65-yard touchdown pass to rookie receiver Charlie Brown. Brown, who spent last year on injured reserve, also had a 45-yard leaping catch among his three receptions (for 124 yards).

Mark Moseley kicked field goals of 43 and 45 yards to give him 10 straight this year and 13 over two seasons. And Mike Nelms' 58-yard kickoff return set up Moseley's field goal in the third quarter that provided the final margin of victory.

But Theismann also had his first two interceptions of the year, ending a streak of 96 passes without one. One came in the second quarter, after Brown's 45-yard catch over cornerback Roynell Young at the Eagles' five.

On the next play, Theismann rolled to his right and passed toward receiver Art Monk in the end zone. But the ball was caught by linebacker Jerry Robinson, who was standing only a few yards from Theismann.

"I never should have thrown it," Theismann said. "If Robinson hadn't intercepted it, it probably would have been intercepted in the end zone. Art was too well covered."

Gibbs: "It was the first time in two years we haven't run on first down that close to the end zone. We thought that pass was a gut cinch for a touchdown, but it didn't work."

Gibbs rightfully was concerned at halftime that the Redskins' 10-point lead wasn't enough, especially after they had outgained Philadelphia, 238 yards to 90, mainly because Jaworski was only five of 17 for 73 yards. Philadelphia also was handicapped by the absence of halfback Wilbert Montgomery, who had bruised ribs.

The Redskins also used halfback Joe Washington sparingly, trying to protect his bad knee on the slippery field. Washington carried once for three yards and did not catch a pass.

The Redskins' offense suddenly lost its continuity after intermission. Theismann, who had completed 10 of 15 passes, couldn't cope with the slick ball or the Philadelphia cornerbacks eliminating short passes over the middle. The Eagles' defense began slanting its front line on almost every play, effectively neutralizing Washington's running game (61 yards for the game). The Redskins gained just 57 yards in the second half and Theismann was sacked three times, choosing twice to go down instead of throwing under pressure.

"Sometimes the offense plays well and sometimes it needs help from the defense," defensive tackle Dave Butz said. "Today, they needed our help."

Until this game, the Washington defense had shown improved aggressiveness, but was inconsistent, ranking eighth in the NFC. But the secondary, which had not had an interception, tipped away a half-dozen balls and had a number of strong tackles to break up other attempts.

Still, Jaworski almost overcame this defensive effort. He directed the Eagles to a 41-yard, third-quarter field goal from Tony Franklin to close to 10-3. After Nelms fumbled the ensuing kickoff, he threw a pass to Billy Campfield for an apparent first down at the Redskin 16. But Campfield fumbled and the ball rolled out of bounds at the 18, bringing up fourth and one.

Eagles Coach Dick Vermeil decided to go for a first down, sending Louie Giammona around right end with a play installed this week. Giammona tried to cut in at right tackle, but was met by cornerback Vernon Dean and linebacker Neal Olkewicz short of the first down.

On the Eagles' next series, Jaworski avoided such a recurrence by getting a score on one big play, a 56-yard pass to receiver Harold Carmichael. White tried to knock down the pass, but when he missed, he was out of position to tackle Carmichael, who ran the final 27 yards untouched. Franklin's conversion attempt hit the left upright and bounced away, and the Redskins still led, 10-9, with 4:29 left in the third.

Nelms then gave the Redskins a much-needed lift. "He won the game for us," Gibbs said about Nelms' long return, in which he almost scored.

"The fumble is God's way of keeping my nose from getting too high in the air," Nelms said. "I just wanted to do something for the Redskins and the fans to redeem myself."

But even with a first down at the Eagles' 33, Washington still had to settle for Moseley's 43-yard field goal. "I shortened my approach a yard and it helped keep my footing," Moseley said.

Now the Redskins had to withstand Jaworski's final assaults. He had the Eagles at the Redskin 15 when he passed toward tight end John Spagnola, waiting in the end zone. Jaworski said the ball slipped from his hands and floated downfield.

"I didn't know whether to shoot it or catch it," Murphy said about the fluttering pass. "I just was trying to get there in time." Murphy did, making a diving interception at the one. Spagnola was five yards away.

The Eagles forced another short punt by Jeff Hayes, his seventh, and Philadelphia had a first down at the Redskins' 38 with time to operate.

After an 11-yard completion to Vyto Kab, Jaworski was sacked by Butz for a six-yard loss. A third-down pass to Carmichael was off target and fell incomplete. On fourth down and 12, the Redskins expected another pass to Carmichael.

Instead, Jaworski looked only to his right, to rookie receiver Mike Quick. The Redskins were using what Peters called "our bread and butter coverage, for the first time all game. The cornerbacks were on the receivers and the linebackers on the backs, and Murphy and I were deep, each covering a half of the field."

Peters began his drop, saw Quick and then saw the pass. He stepped in front of Quick and grabbed the ball, returning it 14 yards to the Redskins' 23 with 1:43 left. The Redskins got one first down on the ensuing series to run out the clock.

"We knew we had to get that first down," said tackle George Starke about John Riggins' five-yard gain on third and three. "(Line Coach) Joe Bugel already had threatened us with our lives, and 1,000 wind sprints Monday if we failed."

"We are really on a high now," Gibbs said. "We feel good about ourselves. What makes me proud about this one is that we had a chance to see if we could play being a favorite. That's a reversal from how it's been in the past, when we've been the underdogs.

"There is something about this team that enables them to come up with a play every time they need it. But we sure want to bring every game right down to the wire. What ever happened to runaways?"