Dave Fish doesn't drink, smoke, chase women, or hit a lousy backhand. On top of that, he has a good sense of humor, is modest about his tennis and squash accomplishments, has boyish good looks, and likes apple pie.

Well, the bit about the pie may or may not be true, but the point is that Harvard's 26-year-old, new tennis and squash coach is damn near perfect.

Fish will need all the perfection he can get to fill the shoes of Jack Barnaby, the coaching legend who retired last year with a long list of national squash championships and Ivy tennis titles to his credit.

To make the picture a little clearer, Fish's mortality was confirmed over the last two weeks as his squash team lost for the first time at Princeton and his tennis squad dropped several matches in a national tournament in Wisconsin.

"I found that taking over after Jack Barnaby, virtually every letter I got said something like, 'Good luck in filling the biggest shoes around,'" Fish said yesterday, adding with a twinkle in his eye, "So I replied that I have only one place to go, and that's down."

"And sure enough...," Fish continued with a chuckle, not finishing the self-deprecating quip.

In fact, though, Dave has been going anywhere but down. Although he may lack the technical genius of Barnaby--who wrote the book, literally, on how to play tennis--Fish has a lot of new ideas about the game and he is beginning to implement them.

"He's trying to add to what Jack did," sophomore tennis player Andy Chaikovsky said yesterday. "Jack was very strong in technique, but Dave's trying to add on the conditioning and mental aspects."

A psychology major in his student days at Harvard in the early '70s, Fish feels that "a great many losses are caused in college athletics by people who are looking for the wrong thing. They're working for the wrong objective, like trying too hard and wanting to win too badly."

"I feel that you can go into it a little deeper," the jeans-and-sweater clad coach continued, "and give a person a way to deal with the ego involvement that hurts his performance."

Working with a grant from the U.S. Lawn Tennis Association, Fish is drawing partly from the Asian martial arts to construct a new kind of athletic program dealing with things like muscle awareness and concentration.

In the meantime, Fish is applying some of his theories to his players, and he has at least one athlete doing yoga exercises.

"I really believe that a lot of these things I'm working on are actually things that Jack did intuitively over the years," Fish said. "I'm just trying to articulate them a little bit more."

Of course, the teams are not about to let their new coach get away with his innovations without a little ribbing.

"The standard joke," says Fish, "is that whenever I introduce a new shot the guys kid me about being 'the guru.'"