The punchless Washington Redskins, still seeking their first touchdown of the preseason, had to settle for two Mark Moseley field goals tonight and fell to a tenacious Denver defense, 13-6.

The Broncos won the game by scoring on the last pay of the third quarter to break a 6-6 tie that had existed since early in that period.

Washington, which beat Tampa Bay, 9-6, in its exhibition opener thanks to three Moseley field goals, never got closer to scoring tonight than the Denver 13. Moseley ended their only two serious threats with successful kicks of 39 and 34 yards, but did not get another try the rest of the game.

The Redskins even put most of their first-string linemen back in late in the game in an attempt to pull out a victory. But quarterback Kim McQuilken could not avoid a savage Denver pass rush and got his club no farther than the Bronco 48 in the fourth period.

Neither McQuilken nor Joe Theismann, who played the first half, had much luck against the aggressive Broncos.

Theismann guided the club to Moseley's first field goal, in the second period, after Washington's No. 1 quarterback was sacked on a third down from the Denver 13.

McQuilken was in charge when Moseley got the tie with 10:09 left in the third quarter. The Redskins had moved to the Denver 18 but elected to run on third and three and were stopped.

This was a Denver team crippled by injuries to its first string running backs. But the Broncos looked far better than Washington on offense, especially in the first half when quarterback Craig Morton easily moved the ball against the Redskins.

Morton should have racked up more than the six points the Broncos had at intermission. The second time they had the ball, he drove them 84 yards for a touchdown on a three-yard run by Dave Preston. But the Broncos were stopped later that half on their 32 and five and Cyril McFall missed two chip-shot field goals.

"We've got to get some touchdowns on the board," said the Redskin Coach Jack Pardee. "We set out to work on some ball control things tonight. I still feel we can get some touchdowns along the way if we can consistently make some short first downs.

"Our short yardage game was more successful tonight than last year. If we keep doing that, we will be a good team later in the season."

Although Pardee talked about his team's few penalties, the Redskins were called for nine infractions, costing them 56 yards. They also botched a punt return and Theismann tossed an interception.

And just one wide receiver, rookie Tony Hall, managed to catch a pass. The other 10 completions went to running backs, tight ends and, on a blocked pass, to center Ted Fritsch.

"The way they were running in the fourth period, the way the whole team played the fourth was encouraging," said Pardee. "I hoped we found something out about our running team. We accomplished everything we wanted except win the game. Our goal was to play a lot of players and look like a decent team doing it."

Still, the Redskins were peppered for 265 yards passing despite six sacks. And they hardly looked crisp on offense, failing time and again to make the big play when it was desperately needed.

Don Testerman, who has been hindered by shoulder and back injuries, was the most impressive of the running backs. Playing late in the game, he bulldozed for 28 yards and picked up a first down on a 10-yard swing pass that should have netted little. But his determination got him to the yard sticks, although he strained his shoulder on the play.

Theismann finished six for eight and 44 yards passing. He was sacked twice for 18 yards. McQuilken completed five of 10 passes for 39 yards and was sacked twice. Nine Redskins caught passes.

Tackle Dave Butz was outstanding on defense, being credited with four tackles and two pass deflections. Reserve middle linebacker Don Hover, who played much of the first half in place of Harold McLinton (who had one interception), had two second-period sacks.

Morton, confusing the Redskins with head bobs and cadence changes at the line of scrimmage, was brilliant. He completed eight of his first 11 passes and mixed his plays masterfully.

On Denver's second possession, he completed passes of 14, 27, 6 and 6 yards to set up a first and goal at the three. Preston, drove off right end past Kenny Houston's desperate tackle attempt for the touchdown. But McFall's point offer failed.

Morton again had the Broncos threatening after a Redskin punt. But linebacker Pete Wysocki knocked down a third-down pass and McFall missed a field goal from the 32.

Theismann then got the Redskins cranked up. John Riggins raced 14 yards for the team's initial first down, 16 minutes into the contest. A 16-yard pass to Benny Malone, who did not start the game after walking out of camp last week, had the Redskins on the Denver 28. After another first down, Theismann couldn't elude a tackle by rookie Rich Tuten on third and six from the 13 and Moseley booted his 39-yarder.

A fumbled punt by Terry Anderson gave Denver the ball midway through the second period on the Washington 34.An interference call on Hover accounted for one first down and an offside penalty on Dallas Hickman helped Denver to another. But Hover overpowered center Bill Bryan and sacked Morton on third down at the five and McFall again failed on a field goal, this time from the 15.

The Redskins tied early in the third quarter after a short punt gave them possession on the Bronco 38. A McQuilken pass to Hall moved the ball to the 25 but the threat bogged down when Clarence Harmon could gain only one yard on a third-and-three. Moseley then was perfect on his 34-yarder for a 6-6 game.

Denver reserve quarterback Norris Weese, scrambling out of the pocket at a moment's notice, had the Broncos on the move again late in that period.

He found tight end Ken Moore open over the middle for 19 yards, then again for 15 on the same play.Former Maryland star Vince Kinney eluded three Redskins to pull in a 26-yarder at the Washington eight for a first down.

Preston, who gained 31 yards for the night on eight carries, bolted for three. He got the call again and, behind a crushing block by guard Tom Glassic on Houston, raced in from the five as the quarter ended. This time, McFall, a native of Ireland, was good on the point after for a 13-6 margin.

Washington ran the ball some more in the fourth quarter but never seriously worried the crowd of 58,799. The Redskins now have a week to work on that unproductive offensive before taking on the Falcons in Atlanta next Saturday.

"I'm just not that unhappy with what I saw," said Pardee. "Now we have a lot to look at on film." CAPTION: Picture 1, Redskins Brad Dusek (59) and Pete Wysocki (50) bring down Bronco tight end Ron Egloff after a short gain on pass play. AP; Picture 2, Redskin defender Joe Lavender brings down receiver Rick Upchurch after a Bronco pass completion.