Reports that the Redskin offense might be offensive this season proved premature last night when Joe Theismann and his mates gave a dramatic demonstration that they are ready for the regular schedule.

With Theismann tossing two touchdown passes and the offensive line dominating the Oakland defense, the Redskins rallied from a 10-point deficit to crush the Raiders, 34-17, before an RFK Stadium crowd of 47,547, the largest preseason gathering here in seven years.

After a slow first-quarter start, Theismann turned red hot, completing nine of 10 tries for 136 yards and both of his scoring passes during the last part of the first half.

But Theismann, as well as he performed, wasn't the whole show. Running backs Buddy Hardeman and Clarence Harmon consistently dashed around the Oakland ends for impressive yards and receivers Ricky Thompson and rookie Zion McKinney made some outstanding catches.

And the Washington front four, after spotting Oakland a 10-0 lead early in the second period, started living in the Raider backfield. The Redskins recorded five sacks, holding Oakland to 54 passing yards while controlling the game after the opening 15 minutes.

Coach Jack Pardee was delighted with the triumph. He said Theismann "was sharp as a tack and Buddy and Clarence were back in form. I was really pleased with our performance."

The only negative aspect to the victory, Washington's thrid straight in the preseason, was the play of the usually impeccable special teams.

Kicker Mike Bragg had one punt partially blocked and another cleanly smothered, leading to a last-minute Raider touchdown. Oakland also nearly returned a kickoff for a touchdown while Washington picked up a penalty on almost every kicking play.

Still, the Redskin offense provided just the medicine the club needed to cure any blahs resulting from last week's lackluste win over Cleveland in which Washington committed so many errors that Coach Jack Pardee called it "Amateur Night."

This was more like Pro Night, especially with Theismann putting on the Redskins' first wide-open passing show of the preseason. The result was a crowd-pleaser complete with enough bobbles to make things unpredictable.

Theismann finished 12 of 20 for 167 yards. He could have done better, but some of his bullets were dropped by his receivers.

No one, however, made many mistakes during the second period, when Washington scored three touchdowns within nine minutes.

Theismann set up the first score with a perfectly thrown 23-yard sideline pass to Thompson that just eluded tyo Raider defenders. Harmon went over from the three to cut Oakland's lead to 10-7.

A sack by end Karl Lorch, who had two for the night, helped get the ball back quickly and Theismann immediately had the Redskins threatening again.

Working from his 36, he found Hardeman drifting out of the backfield. Hardeman caught the ball just ahead of linebacker Jeff Barnes, and then eluded cornerback Odis McKinney to pick up 10 more yards and a first down at the Raider 30.

Before Oakland could collect itself, Theismann went for the touchdown. He was successful when Thompson dove and held onto the ball long enough, deep in the end zone, to be credited with the score. It was now 14-10 Washington with 5:44 left in the half.

A 75-yard kickoff return by the Raiders' Malcolm Barnwell almost cut into the Washington's point parade. But a sack by end Coy Bacon, who also had two in the game, forced a Raider field goal attempt that was unsuccessful.

Washington got the ball with 4:05 remaining before intermission. Zion McKinney pickep a holding call on first down, but a 14-yard pass from Theismann to rookie Art Monk, who made a nifty sideline catch, got things rolling.

Hardeman's 10-yard end run and a seven-yard reception preceeded a 10-yard completion to McKinney after Theismann had scrambled away from big John Matuszak. Theismann came right back to McKinney, the rookie from South Carolina, and picked up 13 more yards and a first down at the 25.

Hardeman accounted for another first down on a six-yard scamper to the 14 before Theismann rifled a pass to tight end Don Warren at the four. With four seconds left, the Redskins disdained a field goal attempt for one last play.

The gamble worked. Theismann dropped back and spotted McKinney running a quick look-in patern. The pass was on target and McKinney held on for the touchdown with one second on the clock. That gave the Redskins a 21-10 halftime lead.

Oakland could never recover from the blitz. The redskins, who scored on a one-yard Kenny King run and a 24-yard Jim Breech field goal before the game was 19 minutes old, stumbled behind second-string quarterback Jim Plunkett in the second half and rarely threatened.

Beech didn't help much by missing three other field goal attempts. His Redskin counterpart, Mark Moseley, was perfect on tries from 43 and 19 yards.

Besides Moseley's field goals, the Redskins also got a second-half touchdown from rookie fullback Ricky Claitt on a one-yard run. That score was set up when Bacon slammed into Plunkett, forcing a funble that Washington's Joe Jones recovered at the one.

Oakland was limited to 202 total yards, thanks in part to five Redskin sacks. But the Raiders also had trouble moving the ball consistently on the ground, a sharp contrast to an impressive last-half Washington running attack.

Harmon, who will begin sharing fullback duties this week with newcomer Wilbur Jackson, picked up 52 on 12 carries. Hardeman added 37 on 16.Hardeman also had three catches for 55 yards. Claitt highligted the fourth period with 52 yards in 13 attempts.

A rash of early game injuries necessitated other lineup switches. Neal Olkewicz left with a probable strained knee, Tony Peters pulled a groin muscle and Dave Butz bruised his ribs.None of the injuries is considered series.

Tackle Terry Hermeling also didn't play after coming down with flu. His place was taken by Fred Dean, who had been starting at guard for the injured Jeff Williams . Gary Anderson took over Williams' position, but even with the two new faces, the line allowed just one sack.

This was also a night in which Benny Malone, the starting halfback last season, did not play, paving the way for his probable departure from the roster this week.

Pardee used his regulars for three quarters, giving them as thorough test, he said, so they can rest more in the final exhibition game at Tampa Bay Friday night.

He also sought a more polished performance than he saw against Cleveland. What he received was a show by the Redskins worthy of a regular-season game.