In two short years, Walter Clark, a 30-year-old Prince George's County school teacher, has transformed the golf hacker's dream into reality: a former high-handicapper, he now shoots regularly in the mid-70s.

Clark is a man obsessed with improving his game. He practices, plays or reads about the theory of the golf swing 13 hours a day. He is a man to no gimmicks. Hard work and dedication are why he has cut his handicap from 25 to 6 in two years.

"Becoming a good golfer is 90 per cent sweat," said Frank Cronin, the University of Maryland pro who launched Deane Beman and George Burns onto the PGA tour.

It took telephone calls to about 30 area golf pros to find a hacker turned good golfer. The criteria was a player who used to have trouble breaking 100 who is now shooting in the mid-70s. Such a phenomenon, the pros said, is as rare as a scratch player. A 6- to 10-shot improvement in two years is considered excellent, they said.

The common denominator for all golfers who show improvement is practice time and a desire to do better. Clark, who teaches social studies and coaches the basketball team at Suitland Junior High, meets both requisites. he either plays, practices or studies golf every day of the year.

But he has also paid a social price in reducing his handicap 19 strokes and becoming runner-up for the Northampton Country Club championship.He is something of a social hermit now, but not by design.

He and some friends drive three hours round trip each Saturday to the Hog Neck course in Easton, Md., a difficult 7,200-yard municipal layout. A couple of weeks ago, Clark and his wife were scheduled to attend a late Saturday night party. He got home from Hog neck at 7 p.m., lay down for a three-hour nap, and didn't wake up until the next morning.

After playing 36 holes on another occasion, he took his wife from their Anne Arundel County home to a fancy downtown Washington restaurant for dinner. Clark fell asleep at the table.

He also finds that his golf has made him a junk-food addict because he does not take the time to eat properly.

Ironically, Clark got into golf four years ago because he had so much time on his hands at St. Mary's Colleg, where he played basketball as a 6-foot, 170-pound guard.

"It was boredom. I really didn't have anything to do," he said. "They had a driving range. So I borrowed my father-in-law's clubs and beat the ball around."

The golf bug trapped Clark within two weeks.

There were only two golf courses near the college and he couldn't get on either - one was military, the other private. So he and some friends put together five or six homemade holes at the driving range.

"We didn't have greens," he said. "We just put a hole and a flagstick in the ground and got the (grounds) superintendent to cut the grass close there. You chipped within a club-length of the hole and then picked up the ball."

When Clark finally got on a golf course, his playing companion, a man who shot 95 on an average day, gave him 15 strokes for the 18 holes, calculating that Clark would shoot 110. Improvement was not swift, although Clark is a good athlete. Two years later, he still had trouble breaking 100.

Then a friend told him the only way to improve was to take lessons. Clark went to Ron Scales and Randy Hoffman at Maryland and Brian Stable at Northampton. He quickly dropped to a l6 handicap, then to 19 last summer and now is 6.

"I was introduced to the basic inside-out swing," said Clark. "I have books stacked high, I still don't understand the swing fully."

But he is progressing. He tries to play with better golfers in order to improve his game. He wants to cut his handicap still more and may join Crofton Country Club next year so he can play in District Golf Association tournaments. Northhampton is not a member of the District or Maryland golf associations.

"What I need is competition from good players in order to work on my game, to learn from them to get my handicap down," he said. "There's so much more I want to learn."

"I'm hitting the ball as well as any scratch golfer," Clark added. "But I'm not thinking like a scratch golfer. The game is so mental; it's too bad you can't measure it."