Professors Cookson and Persell have not set out to write another Preppies 'Handbook here. They have more serious matters in mind than monograms and madras. What they intend--and what they've been able to produce with a good deal of success--is a sociological/statistical investigation of the whole boarding-school phenomenon, its origins and development, its mores and its probable future. Less than one-percent of American students of high-school age are educated in the nation's elite boarding schools. In researching their book, Cookson and Persell queried several thousand of these students at 57 schools in 15 states. Teachers, headmasters, administrators and trustees, parents and alumni were also interviewed concerning their work, their goals, their attitudes. What became apparent during the course of the investigations was that elite boarding schools now face a philosophical crisis. The original objectives of such elitist education--producing a powerful but guilt-free privileged class through self-denial and noblesse oblige, and preserving that class through the development of common cultural standards--are being challenged, not so much by the underprivileged but, more dangerously, by the Preppies themselves. Self-denial is ""out""; hedonism, narcissism and materialism, ""in."" Privileged preppies pool their pocket money and send two classmates to Venezuela to bring back a supply of coke. Alcoholism is rife, attempted suicide not uncommon. Instead of ""public service,"" ""venture capital"" inspires the young and affluent. Rousseauian ideals and ""Me Generation"" realities are on a collision course on the manicured campuses of Choate, Groton, Miss Porter's and the rest; they have, in fact, already collided. The promise of ""future gain"" fails to compensate for ""present pain"" these days. Traditionalists may sing those old Spenglerian blues, but for such clearsighted critics as Cookson and Persell, there doesn't appear much hope for those they call the ""prisoners of their class."" The prognosis is far from promising, but Preparing For Power, by avoiding jargon and by buttressing its speculations with facts, makes its points convincingly.