EVERYTHING TO GAIN Making the Most of the Rest of Your Life By Jimmy and Rosalynn Carter Random House. 198 pp. $16.95

Jimmy and Rosalynn Carter were relatively young -- he was 56, she 53 -- when the voters of the United States sent them into early retirement. In January of 1981, after four years in the White House, the Carters headed back to their ancestral home in the Georgia hamlet of Plains and to a future, in the former president's words, that seemed bleak. After an enervating trip to Europe to welcome the newly freed Iranian hostages, Carter "returned to Plains completely exhausted, slept for almost twenty-four hours, and then awoke to an altogether new, unwanted and potentially empty life."

The reasons for the Carters' initial depression are hardly difficult to fathom. For years they had been at the center of vigorous political activity, first at the state, then the national level, and their term in the White House had been marked by sufficient drama, accomplishment and disappointment to leave them accustomed to great events. Yet now, in what should have been the prime of their mature lives, they were being relegated to what gave every appearance of being their "sunset" years.

But neither the former president nor the former first lady is one to sit idly by while the rest of the world works busily away. Instead of slipping into their rocking chairs, the Carters have led active, productive "retirement" lives that, by their own account, have been fulfilling and satisfying. They have both published memoirs, they have undertaken a wide variety of hobbies and domestic chores, they have traveled around the world on behalf of various good causes, and they have participated in the Habitat for Humanity program devoted to reconstructing dilapidated inner-city houses.

Now, not surprisingly, the Carters have written a book about their postpresidential years. It is a curious production, half memoir and half self-help book. It offers a good deal of sensible advice, all of which should have already occurred to anyone who thinks reasonably carefully about life's risks and rewards, and it is padded out with anecdotes and reminiscences that are rarely of more than marginal interest. The Carters' good intentions are self-evident throughout; so too is the humorless good humor that, in retirement as in the White House, is the essence of the Carter style.

"As we approach retirement age," the Carters write, "it is natural to have more frequent and somber thoughts about the end of our lives, although all the great religions teach us not to fear death. But perhaps it is even more important not to be afraid of advancing age. This late period can be a time of foreboding and resignation, a time merely of assessment and contemplation. But it also offers the chance to be bolder than ever before and to do worthwhile things that have been avoided or postponed for five or six decades. To take that chance is what this book is really meant to encourage."

Thus, the Carters go on at some length not merely about the good works to which they have devoted themselves -- they are ardent supporters of volunteerism as a retirement activity -- but also about such twice-told tales as how to keep body and soul in peak condition. Their nine rules by which "most of us can put ourselves in control of our life span" are all eminently sensible ("Fasten seat belts"), eminently predictable ("Do not smoke"), and can be pasted on the refrigerator for easy reading ("Minimize consumption of foods high in cholesterol and saturated fats, sugar and salt"). You will be forgiven if you think you read them first in Woman's Day.

The Carters are so doggedly earnest about all this, so perky and pious and correct, that it affords me no particular pleasure to point out what by now must surely be evident, namely that "Everything to Gain" is a stuffy, self-righteous book. The Carters mean well -- they also mean to make money -- and for this apparently we are to be both grateful and respectful, but it remains that "Everything to Gain" has no more to offer than any level-headed article in a supermarket magazine. Beneath its piety lurks a strong strain of self-congratulation, and beneath its concern for others lurks the sanctimoniousness of the homilist.

Yes, the advice the Carters offer is useful if pedestrian, and the example they present of two people who have refused to capitulate to defeat is admirable. But there are many other places where one may find the same advice, and an exemplar that insists on shining a light upon itself is somehow uninspiring. Inasmuch as the Carters acknowledge that, in retirement, "our financial resources would be adequate to meet our needs," one can only ask: Was this book really necessary?