The underdog Houston Oilers might have held their most enjoyable practice today since the start of training camp.

Fullback Earl Campbell ran like a frisky colt and quarterback Dan Pastorini threw his first passes in almost two weeks.Teammates realized that those were sure signs their two pivotal players have recovered enough from injuries to play in Sunday's American Football Conference title clash at Pittsburgh.

The club's mood was a happy contrast to the gloomy atmosphere that hung over the Oilers last Saturday in San Diego. And no one was more depressed than Pastorini after desperate 4 a.m. treatment on his sore groin failed nine hours before the start of the AFC playoff game against the Chargers.

"There was no hope and I knew it," Pastorini said, recalling how the groin was still too swollen and discolored to allow him to play.

Campbell thought, until just before kickoff, that he could start. But after testing his pulled groin in warmups, he was quizzed by Coach Bum Phillips.

"Is it 100 percent or can you feel it pull?" asked the coach.

"I can feel it a little," replied the player.

Like Pastorini, Campbell never played against the Chargers.

Split end Ken burrough had, besides his own groin pull, a more troublesome tailbone bruise. He convinced Phillips to play him in the second half, but was used only as a decoy.

Without these three stars, the heart of their offense, the Oilers somehow managed to stun the football world by upsetting the highly favored Chargers, thought by many to be the potential Super Bowl winners.

Yet now the Houston victory seems matched in importance by the fact that Phillips refused to use his injured players on a day when defeat meant the end of the season for his club.

In football it's macho to play when hurt.

"There is no tommorrow," says the coach, explaining why Joe Hero limped off the bench and made the crucial fourth-period carry.

The movie "North Dallas Forty," attempted to portray one way NFL teams handle injuries.

"That's the movies," Phillips said today. "This is real life. Hell, John Wayne won every fight in the movies, too. But That's not how things work."

Phillips gambled. Perhaps he alone was convinced the Oilers had a shot at beating San Diego without Pastorini, Campbell and Burrough. If he was right, and if the three got another week's rest, he might have a nearly healthy club ready for the AFC title game. If he was wrong . . .

"There wasn't any question of right or wrong," he said. "I made a decision and that's all there is to it.

"Let's face it, the team wanted them out there, but the team wanted them out there if they could help. What was the use of playing someone if they couldn't function correctly.We have more faith in our backup people than that."

But wasn't he tempted to turn to Campbell down at the San Diego goal line in the first half and say, "Earl give me one yard and a touchdown?

"Nope," Phillips said running his hand over his forehead "Once they were out they were out.

"I never said, "Well, in the fourth period or in the clutch they can play. There were no exceptions involved. if they were capable of playing, they would play right away or not at all."

The bottom line, according to Phillips, was this: "I was thinking about their future, not ours."

He explained: "Why take a chance? I'm not going to take a chance to ruin their futures or anyone else's. They could have really messed themselves up just because I was selfish enough to play them in one game. No way.

"The people I feel most sorry for are the two players (Pastorini and Campbell), not the rest of us. The other guys could get into the game and do something about winning and losing. You can put the blame or praise on your own shoulders.

"But here are two players who have practiced and trained for 25 weeks and to get this far and not be able to play, that's really hard. When you get to this stage, you hope you can contribute something. If you can't, you feel like you are letting everyone else down and there is nothing you can do about it."

During the game, Campbell twice asked Phillips to put him in. Of the three, he had appeared the most likely to play considering his progress during the week. But Phillips refused to budge.

"It was too big a risk," Phillips said. "If he had played and torn the muscle, calcium might have formed. A chronic problem might have developed.

"Yes, I realized he probably was maybe 90 or 95 percent okay. That wasn't good enough. It had to be completely right."

Burrough, like this teammates, had been receiving special treatments all week from the team chiropractor. He improved enough to be used although he couldn't stretch out to full speed.

"It felt good to contribute in any way I could," he said. "And I think I helped some people get open. The first play I was in, they held me (for a first down at the 50).

"After that, I would hear their secondary talk about covering me. I know they were thinking and that was important."

It wasn't the first time Phillips had employed a receiver as a decoy. Mike Renfro, who caught the winning pass in the San Diego game, had a weak knee earlier in the season and although he played regularly through the first 12 contests, he caught only one pass, mainly because the coaches did not want to risk further injury with unnecessary contact.

Nor was this the first time Phillips had taken a hardline approach to injuries. When standout tackle Greg Sampson had a serious head injury prior to this season, Phillips ruled him out of football although others have come back from similar problems.

"I wouldn't play my own son if he was hurt like Greg, so why should I play somebody's else's son?" asked Phillips.

Now Phillips enters the AFC title game against Pittsburgh with a team that has played the last six quarters of the playoffs without either its best quarterback or the No. 1 rusher in the NFL. Yet the Oilers are still alive and there appears to be an excellent chance the stars will be available Sunday.

Campbell ran near full speed Tuesday and today during workouts and Phillips is convinced his fullback is almost at top form.

Pastorini wasn't supposted to test a few snaps and toss a couple until Thursday, but took passes today in practice. Burrough loosened up, although Phillips won't let him "go all out until Friday or so. No use pushing it too hard."

So how does Phillips feel now about the events of the past few days?

"Well, all last week I thought that the three would play and I kept saying it and look what happened. But I've got to be more optimistic right now.

"Earl is running real well and last week Dan couldn't even move well enough to get behind a center, much less throw a pass. To my way of thinking, that's a whole lot better."

That's how Pastorini also looks at it.

"That game Sunday was the longest of my life," he said. "I was useless. But now the Oilers have shown they can win without us. I think that's great for eveyone."

Punt returner Richard Ellender was the only Oiler listed today as unable to play in the AFC championship game.