New insights on Adamses; Descent from Glory - Four Generations of the John Adams Family, by Paul C. Nagel. New York: Oxford University Press. 400 pp. $25.

Paul C. Nagel's splendid scholarship illuminates often-dark aspects of the private lives of John and Abigail Adams - and of three succeeding generations of their family.

By so doing, it provides perspective to enlighten today's Americans about more than just one renowned couple's family. We learn that 19th-century parents dealt with helping troubled children. And we discover yesteryear's adults, too, found that their elderly parents required much loving attention. These historical perspectives are welcome.

So, too, are the full views of the famous Adamses - John, Abigail, and son John Quincy. The larger-than-life stature so often accorded our early presidents for their professional accomplishments too often hides lack of knowledge of their private sides. It is good to learn, for instance, of the mellowing of the once-unbending John Adams, the nation's second president, and the warm, grandfatherly support and friendship he ultimately provided succeeding generations.

Mr. Nagel is to be commended for his willingness to read what must be mountains of previously sealed Adams family letters, on which this book, in part , is based. Yet the organization he chose - dealing with a bewildering number of family members over four generations - is difficult for the reader. Characters and details blur by the time the book is half read; it would have been better to concentrate on fewer people, and in more depth.

There are other deficiencies. A reader yearns to savor those extraordinary family letters which are excerpted in snippets. To relate the Adams family's attitudes to its times, sketches of the mores of 19th-century America are needed. And, since the book focuses on inner conflicts and faults of individuals , too negative an impression of members of an extraordinary family remains at the conclusion.