When Navy opened football practice this morning, not one of the four secondary positions was manned by a 1981 starter.

Two regulars, Elliott Reagans and Rusty Smith, graduated in June. Jeff Shoemake, his knee badly torn against Notre Dame a year ago, was forced to give up football. Ray Daly resigned from the academy.

For further aggravation, one of the more impressive spring fill-ins, Dave Tolliver, was a victim of academic problems. So Navy's new coach, Gary Tranquill, and his secondary assistant, Nick Saban, were faced with a giant headache until a remedy suddenly appeared at hand.

Cornerback Jon Ross, a three-time letterman who was to have been a 1981 cocaptain, is back in school after a year spent as an enlisted man on a diving tender in Newport, R.I. If Ross had any questions about his reception, they were quickly dispelled by a delighted coach and smiling teammates.

"It's a damn good thing it happened," Tranquill said. "We were thin back there and then we lost the two guys who got most of the work in the spring, and they were young anyhow. Jon Ross gives us some experience and some leadership. He's a bit of a fireballish type of guy."

If the Midshipmen are happy to see him, Ross is doubly glad to get what he calls a "second chance."

Ross was forced to resign from the academy in June 1981 for a violation of the honor concept. He had written unauthorized notes in a textbook he was using during an examination. Although most schools would treat such an occurrence lightly, it meant goodbye to the Naval Academy.

Reduced to enlisted status, Ross had only one goal in mind: to win readmittance to the academy. While impressing his bosses with his industry, he also bought a membership in a fitness club and worked out on the equipment. He watched some of Navy's games, both on television and in person, and tried not to feel sorry for himself.

"It was a learning experience," Ross said. "I tried not to get in a frame of mind where I wished I was out there. It was a chance to watch from the stands for the first time, since I had played as a plebe, and I was able to pick up things and learn from it. It motivated me to keep working out, in case I could get back in the academy and play again."

Last month, with nothing but favorable recommendations on the table, the academic board reviewed Ross' case and invited him to return.

"I came in for summer school and I've been watching films and working out for three or four weeks," Ross said. "I've just been backpedalling, stuff like that. My speed has dropped a tenth, from 4.6 to 4.7, but on the whole I feel pretty good, better than I thought.

"Today, the reading was the toughest thing to adjust to. There are some differences in the system and I have to learn new reads, but basically it's the same. I feel I've pretty well caught up to everybody.

"I just want to do the best I can, whether direct playing or helping out the younger guys if somebody beats me out. I know what it takes to practice and I know how to get players motivated. I'm a little more intense this year, because it's my second chance at my last year in football. Not many guys get that chance."

The welcome from his teammates has helped to ease Ross' return to the academy.

"Most people have been very positive and they've told me they're glad to have me back," Ross said. "I was a little leery about it, but people at the academy are of such high quality that they don't hold things like that against you."

When Ross left here 14 months ago, he showed himself to be of high quality, too. Rather than hide behind the secrecy act, which could have masked the reasons for his absence, he issued a statement explaining the circumstances surrounding his abrupt departure.

"I felt, since I had been elected cocaptain, I had an obligation to inform people," Ross said. "It cleared the air and avoided a lot of unpleasant speculation. You have to accept responsibility for what you do."