The Houston Oilers' visit to Three Rivers Stadium today was an exercise in claustrophobia. They were smothered by the Pittsburgh Steeler defense.

En route to a 38-7 reinforcement of their stature as the best team in the National Football League, the Steelers dealt out inadvertently cruel and unusual punishment on the Oilers.

Quarterback Dan Pastorini suffered an aggravation of his tender throwing shoulder and will miss a game or two; Billy (White Shoes) Johnson suffered a torn knee ligament and will be lost for the season, and Earl Campbell's posture was damaged when he was held to 38 yards rushing in 16 carries and was kept out of the fourth quarter, to spare him further pounding. That was the lowest output of Campbell's professional career, now into its second year.

The Oilers are left with two quarterbacks in Pastorini's absence and Gifford Nielsen hit on only four of 11 passes after replacing Pastorini today.

He got off a nine-yard scoring pass to substitute wide receiver Guido Merkens with three seconds remaining to avert a shutout. That was risky, because Merkens is the only other Oiler with a background as a quarterback. He was listed as No. 3 today.

Coach Bum Phillips and the Oiler assistant general manager, Pat peppler, were asked separately if the club might try to sign another quarterback, such as former Redskin Billy Kilmer. Both said they had no plans to, at least until the extent of Pastorini's injury is fully determined.

The circumstances of Pastorini's exit from the game midway in the third quarter prompted serious concern because he was taken off the field on a rolling stretcher.

Attempting to pass from his 20-yard line on second and 20, Pastorini was chased out of the pocket and rolled to his left.

Linebacker Loren Toews hit his right arm as he raised it to pass. Defensive end John Banaszak, 6 feet 3 and 244 pounds, intercepted the aborted throw and Pastorini was hurt when he tackled Banaszak, who fell on top of him.

Pastorini's injury first was announced as a "badly jammed right arm." In the dressing room, Dr. Tom Cain called it a "badly contused shoulder" and estimated the quarterback would miss one or two games. X-rays were negative.

Pastorini had played in only three periods of the Oiler's four exhibition games because of injury to his shoulder blade. He had been wearing a brace to hold the blade in place. He also wore a flak jacket again today and when he left the dressing room, his right arm was immoblilized in a shoulder brace.

Wide receiver Johnson was injured from a tackle by Steeler cornerback Ron Johnson after returning a punt. Dr. Cain said Johnson had a torn ligament in his right knee and would undergo surgery that would sideline him for the season. The speedy game-breaker underwent surgery on his left knee last year.

The taciture Campbell, a 166-yard gainer last week against the Redskins, said of his experience today, "I've had better days in sports."

Pittsburgh leader Terry Bradshaw threw two touchdown passes in completing 12 of 29 throws for 198 yards, while Steeler defenders shut off Pastorini with four completions in 16 attempts for 16 yards. He was intercepted three times and sacked five times.

For the second straight game, second-year running back Sidney Thornton scored twice, on a 16-yard pass from Bradshaw and on a one-yard plunge. Franco Harris led the rushers with 42 yards in 14 carries.

The Steelers controlled the Oiler offense although playing without defensive linemen L. C. Greenwood, Dwight White and Gary Dunn, who had done so well in place of Joe Greene on Monday night in an overtime victory over New England.

Phillips said, "The Steelers' defenders are a whole lot stronger than they were last year. We couldn't block them. They just dominated us."

His acknowledgment came on top of those by New England Coach Ron Erhardt and quarterback Steve Grogan, who both said the Steelers exerted so much pressure Monday night the Patriots could not do what they wanted.

In the first quarter, Campell was thrown for a three-yard loss by linebacker Jack Lambert. On third and one in the second quarter, Campbell was stopped cold one on one by defensive end Tom Beasley, playing in place of Greenwood. On third and one in the fourth quarter, quarterback Nielsen denied Campbell the ball and merely had him fake a run for a pass that failed.