After high school, Charlie Thornton was resigned to giving up football. Even he thought he was too small. He was better at math.

But now, "Thunder" Thornton leads his football team in tackles, playing at Navy, of all places.

Not many students at Compton High School in the predominantly black community of Compton, Calif., considered going to the Naval Academy.

Thornton's friends thought he had enlisted.

"They thought I was just going into the regular Navy," said Thornton. "A lot of people in California didn't know there was any such thing as the Naval Academy."

But Thornton, a B-plus high school student, heard about the academy from his football coach, who also happened to be his math teacher.

"I applied to USC and UCLA, but I thought, why not go away from home?" said Thornton. "I came here for academic reasons. My coach said it was a good school, and it wouldn't hurt me financially."

After a year of prep school, Thornton enrolled at the academy and settled nicely into the strict routine. Thornton's home had not been a highly disciplined one, but it had been a trouble-free one. His sister is a doctor. His father, a foreman at a meat company, "let us do what we wanted."

What Thornton wanted at the academy was math courses.He had no particular problems adjusting to the vastly different environment, although he remembers being slightly homesick his first year.

"I have pretty good friends here now," said Thornton. "Back home, my school was all-black, and I really didn't know any white people. But I didn't have anything against them, and I really had no problems here.

"As for the discipline, it's discipline you can put up with."

His first summer here, however, he found that he "wanted something to do.

"And football was the only sport I had any experience in," said Thornton. "So I asked about trying out for the team, and at first, the coach said he didn't think so."

Thornton persisted and played well enough on the plebe (freshman) team to be recommended for the varsity. Last year, as a sophomore, he started the last five games at detensive end, where the Mids suffered many injuries.

Thornton had played linebacker on the plebe team but had been an end in high school, so the switch was one he enjoyed. It was Thornton's quarterback sack at the Navy 16 that helped the Mids protect a four-point lead and beat Georgia Tech in a game witnessed by President Carter.

This year, due partly to an easy opening schedule, Navy is tied for the national lead in scoring defense, having blanked Virginia, 32-0, and Connecticut, 30-0, in the first pair of back-to-back shutouts at Navy since 1957.

Thornton had 12 tackles last Saturday against Connecticut and was named to the weekly All-Eastern College Athletic Conference team.

"I am kind of surprised. I never thought I'd be playing football any more," said Thornton, who was beeted up to 202 pounds, up 22 pounds from his freshman year, thanks to weight training.

"I'm playing with more confidence. Last year, I had to prove I belonged out there. This year, I know my abilities."