Irish Are Irish at Finish : Notre Dame: Much-maligned defensive unit finally comes together and plays a complete game.

Nothing has come easy for the Notre Dame defense this season, except giving up yards, points and, when it mattered most, a game or two.

This is the defense that made Michigan’s rushing attack famous. Remember--253 yards? The Irish can recall every embarrassing inch of it.

This is the defense that allowed Purdue 354 passing yards . . . permitted Stanford to complete 26 of 34 passes and rush for five touchdowns in the Cardinal upset . . . watched Miami pass for 355 yards and run for 118 yards . . . gave up 221 rushing yards and four touchdowns to Navy-- Navy . . . allowed 516 yards to Tennessee . . . made Penn State look like BYU, what with the Nittany Lions’ three touchdown passes. Not surprisingly, the Irish lost the game.

If you need a reason why Notre Dame Coach Lou Holtz looks as if he has aged 10 years in one season, the play of the Irish defense is a smart place to start. The final figures haven’t been calculated, but team officials confidently predict that the 1990 Notre Dame defense will allow more yards per game than any in its history. That goes back to when the Irish wore leather helmets.

“Usually we’ll play well for 50 minutes, and then we’ll have a 10-minute break where teams will score a lot of points,” said Todd Lyght, Notre Dame’s All-American safety.

The same was expected Saturday as the Irish faced USC and quarterback Todd Marinovich, who picked apart Notre Dame for 333 yards and three touchdowns in last year’s game. And that was against an experienced Irish defense. Just think of what he would do against these guys.

Marinovich had his moments Saturday, but few of them translated into points. He completed 26 of 39 passes for 273 yards, but not one of them resulted in a touchdown.

The Trojans gained yards--lots of them--but scored few points. All they had to show for their troubles were two field goals and a 10-6 loss to the Irish.

“It was,” said Notre Dame nose tackle Chris Zorich, “a very impressive game.”

Zorich would know. He had eight unassisted tackles and one sack. The sack, though, came on the final play of game, as Marinovich searched desperately for an open receiver. It is a sack, Zorich said, that he will always cherish, what with this being his last regular-season game.

“It was incredible,” he said. “I lined up and said my prayer: ‘I want to make this play, I want to make this play.’ ”

The six points were the fewest Notre Dame has allowed all year. For a change of pace, the Irish prevented a team from converting third-down plays at will. The Trojans managed to make only seven of 16.

The Irish defense could do little wrong. It forced the Trojans to settle for a field goal after USC had first and goal from the nine.

It sacked Marinovich six times.

It prevented USC from making a first down when it counted most: fourth and 11 and only 1:13 remaining in the game. Lyght knocked receiver Gary Wellman out of bounds a yard shy from the first-down marker.

“USC, when they’re in a tight situation, they go for the exact number of yards they need,” Lyght said.

True to form, the Trojans did as expected. Not true to form was what happened next: Notre Dame stopped them.

“This is the tightest we played, except for maybe the Miami game,” said linebacker Scott Kowalkowski. “We finally jelled. We weren’t so conservative, and we blitzed a lot more.”

His teammates said this was the first truly respectable defensive game the Irish have played all year.

“We’ve come out and played well on first and second downs, but on third downs something would happen,” linebacker Michael Stonebreaker said. “This time we finished them off.”

Said Lyght: “We really hadn’t put together a 60-minute ballgame.”

There are mitigating factors. Three games ago, freshman free safety Willie Clark was a running back. That’s before Holtz “suggested” that Clark try playing defense.

“But he said (I) could come back to offense at the end of the season,” Clark said.

Fat chance. Clark had three tackles and broke up one pass against USC.

There were other problems. Lyght has been hurt. The secondary was awful, thanks to the loss of three starters. Two new defensive coaches had joined the team at season’s beginning. Not exactly the formula for success.

But Saturday night all was well again. The Irish were, well, the Irish again.

“We know we have a good defense,” Clark said.

At last, they proved it.