The Dallas Cowboys advanced to the Super Bowl for an unprecedented fifth time today with a devastating defense that was mostly responsible for a 28-0 victory over still another frustrated Los Angeles Rams football team.

Cowboy safety Charlie Waters' two interceptions set up Dallash first two touchdowns in a 28-point second half, though most of the Cowboys were pointing toward a fourth-and-one tackle by Dallas rookie Larry Bethea late in the tird period as the game's turning point.

"We've reached the goal they set for ua back in training camp," Waters said in a cramped Cowboy dressing room. "They ingrained it in us -- that we could be the first to get there five times. They also talked about being the first to win three Super Bowls. And now we can do that."

The Cowboy victory over a team that lost this NFC championship game for the fourth time in the last five years advanced the defending world champions into a Super Bowl game aginst the Pittsburgh Steelers in Miami on Jan. 21.

The winner will be the first team to win three Super Bowl titles.

The Rams went home today mostly because their offense went nowhere except toward the X-ray room. Starting fullback John Cappelletti suffered a separated right shoulder late in the first quarter and quarterback Pat Haden a compound fracture of his right thumb late in the third period.

Both men were victims of whacks administered by Cowboy defensivce tackle Randy White, a former Maryland man. Neither Cappelletti nor Haden returned to action after their injuries, and the Rams dearly missed them both.

Describing his tackle of Cappelletti, Shite said, "I caught him from behind and he must have fell wrong. He caught the pass (15 yards) and I don't think he saw me ciming and cut back. I didn't know until after the game that he was hurt."

Haden was hit by White as he threw what turned out to be the second interception by Waters.

"I didn't hit him as hard as I could. I had my arms up and was trying to hold up," White said. "Maybe he was hurt when he fell. I didn't know about it until our defense started talking about how to work against (Vince) Ferragamo."

Waters, meanwhile, picked off both his passed in the third quarter after recovering from a knockour kick he suffered tackling Haden in the second quarter. "I was kinda woozy for awhile," he said, "but I remember the interceptions."

Both pickoffs were intended for Ram tight end Terry Nelson in the left flat, and both were returned deep into Ram territory. Waters' first interception and 20-yard return to the L.A. nine set up Tony Dorsett's five-yard touchdown run with 10:11 left in the third period for a 7-0 lead.

His second interception and return of 29 yards to the Ram 21 led to the second score, a four-yard touchdown pass from Roger Staubach to fullback Scott Laidlaw with 14/02 left in the game.

Samdwiched in between these two interceptions was Bethea's big hit on reserve Ram running back Jim Jodat, playing in place of the injured Cappelletti.

At that point, the Rams were trailing, 7-0, and had excellent field position because of a 23-yard punt return to the Dallas 23 by Jackie Wallace.

It was fourth and about a foot at the Dallas 14, and Bethea was in the game in place of all-pro defensive end Harvey Martin.

"Harvey's been hurt all year and they had enough faith in me to use me in short yardage and goal-line situations since about midseason," said Bethea, a Cowboy No. 1 draft choice in 1978.

That faith was more than justified when Bethea beat all-pro offensive tackle Doug France at the snap of the ball and plugged the hole Jodat aimed for. "I hit him with my shoulder," Bethea said, "and he bounced back. Bob Breunig finished him off, but that was me on the hit. Did I look good on television?"

Yes, and in person, too.

Several Cowboys questioned the Ram strategy in going for the first down instead of the field goal. "I was surprised, I wouldn't have doen it," said defensive tackle Larry Cole. "But I'm glad they did. We just never thought we wouldn't stop them."

Ram Coach Ray Malavasi defended the decision to go for the first down. "We went for it because we wanted a touchdown," Malavasi said.

"I had told the team the night before that we would go for it if we got in that situation. We had a shot to make it but our back did not hit the right hole. The hole was to the left and he ran it up the middle,"

Waters' second interception came two minutes later, and came about mostly because the Cowboys faked a miximum blitz on Haden.

"Pat thought we were coming and he threw it real fast," Waters said. "We had doubled up both wide receivers and I had the tight end (Nelson) man-for-man. We just forced him into making that play. That's how our defense operates."

Staubach's touchdown pass to Laidlaw followed that interception. but the Cowboys still were not safe, particularly when Haden's replacement, Vince Ferragamo, connected with Willie Miller on the Rams' most spectacular play of the day.

Midway through the fourth period, Miller caught a pass on the left sideline, eluded a diving tackle by Aaron Kyle, and scooted to the Cowboy 10 on a 65-yard play.

But the Rams' frustrations hit their peak on the very next play. Tailback Cullen Bryant fumbled a routine handoff and the ball popped into the waiting arms of Cowboy defensive end Harvey Martin. End of threat. End of scare.

Staubach, who had two of his passes intercepted in the first half, elected to hand the football off to Tony Dorsett on first down, and the little tailback gained 53 yards around left end.

Six plays later, Staubach passed 11 yards to a touchdown to tight end Billy Joe DuPree with 2:56 remaining for a 21-0 lead, and most fans in the crowd of 67,470 began heading to the exits.

They had the misfortune of missing the Cowboys' final and rather fitting fourth touchdown. Thomas Henderson, the loose-lipped linebacker who had described the Rams earlier in the week as chokers, provided the coup de grace with a 68-yard touchdown return of a Ferragamo pass intended for Jodat.

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