The title is more than a tennis phrase. Mr. Ashe, the young Negro tennis internationalist, Davis Cup player and potential super-great, humbly acknowledges that he has received advantages that he could not have expected. Recalling a civic celebration in Richmond honoring him, he writes, ""Tennis has turned me from a nobody into news. Instead of a field hand...I was a university-educated world traveler."" The son of an upright, hardworking couple, he was ""adopted"" from the age of ten by a number of people who brought him up, and, more importantly, taught him the fine art of tournament tennis and made him sweat enough on the practice court to float him well up in the world standings. Ashe, who has a fine reputation as a man and as the ""racial symbol"" he calls himself, has produced a sensitive book combining modesty, pride and a sort of relentless realism. It is a book to be enjoyed by anyone who hopes and often believes that nice guys finish first. Not until after two years of Army service will we know whether the Jackpot is for him.