Last fall, the Harvard football team returned starters a five of the six offensive skill positions, but by the end of the season a potentially explosive attack had dwindled away to practically nothing.

The loss of wide receiver Jim Curry didn't help, but the key factor was that without the fine 1975-edition offensive line, which had been wiped out by graduation, quarterback Jim Kubacki was simply not the same run-pass threat he had been the year before.

In any team sport, one weak link can curtail the efforts of the other players, and Crimson coaches are hoping that this won't be the case with the current edition of the Harvard defense. Sure, Joe Restic has welcomed the Ivy League's best defensive line back into the fold along with a potent pack of linebackers, but "unless the defensive backs can handle the one-on-one coverage, we can't do what we want with these other people. We can't use the blitz; we can't put pressure on the opposition," Restic said yesterday.

And the task of patrolling the deep positions, where one mistake can mean six points in a hurry for the opposition, has fallen on a talented but very inexperienced crew.

All four of last year's starters, safety Bill Wendel, "adjuster" Lou Rice, All-Ivy team captain Bill Emper, and the late Andy Puopolo, cornerback, were seniors.

Paul Halas, an unsuccessful quarterback candidate two years ago, lettered last season as a reserve safety. This time around, he has the job to himself. He came through against Columbia, picking off two Lion passes. "He was on top of every situation," defensive backfield coach Larry Glueck said yesterday.

The vital adjuster spot was held down by senior John Tuke. A heavy hitter who Jettered as a speciality team player in 1976, he has had to work hard on his pass coverage to earn the starting berth.

Four different juniors shared the cornerback duties on Saturday: Steve Potysman, Fred Cordova, Dave Kinney, a converted split end, and Al Ippolito, who came out of nowhere to earn a regular spot by losing 10 pounds over the summer.

The use of four different players was partly the result of enviable depth, but both Potysman and Cordova left the game early because of injuries. Potysman might miss Saturday's contest.

The opening-day performance of these pigskin neophytes was very impressive. Ippolito added an interception to Halas' pair, and Columbia managed only one long gainer in the air.

Indeed, the only problem with the performance was that it came against a floater-throwing Lion quarterback. With any luck, Harvard would have picked off another three or four of his passes, Restic said.

The deep backs answered the first question, but it was an easy one. The test will surely get harder in the weeks to come.