It is only natural, but not many people under the age of 35 know or care about Franklin Delano Roosevelt. Teddy Roosevelt is as remote as Thomas Jefferson. Even more distant and irrelevant are the relatives and friends of the two American heroes.

While 35-45 is a gray area, most Americans over the age of 45 have an intense gut reaction toward the family, usually toward FDR. Witness the ferocity of the debate about whether Ronald Reagan can legitimately claim to be FDR's legatee.

None of these books is meant as an introduction or as a primer for the younger person with little background. All assume broad knowledge of at least one bygone era.

The one which could most closely touch a young reader is "One Third of a Nation." It is a collection of reports filed by Lorena Hickok, who as Harry Hopkins' "confidential investigator" toured the country by car from 1933 to 1935 so that Washington could get a firsthand picture of the condition of the country. Undoubtedly, some people will pick this book because of the recent speculation on her relationship with Eleanor Roosevelt. But the high quality of this book shows that Hickok should be recognized in her own right.

Hickok's U.S.A. is real and sad. Characters are individual poor people, not faceless statistics. While her reports are not as striking as, say, George Orwell's contemporaneous picture of England in "The Road to Wigan Pier" or "Down and Out in Paris and London," there are compelling passages:

"On one of the trails we met an old woman, they called her Aunta Cora. Half dead from pellagra, she stumbled along on her bare, gnarled old feet, clutching under her arm a paper bag containing a few scraggly string beans she'd begged off somebody.

"I stopped and talked to her. As I started on, she reached out and laid her hand on my arm and said in a voice that was hardly more than a whisper:

'Don't forget me honey! Don't forget me!'"

Or in North Dakota: "Into the relief office in Williston came today a little middle-aged farmer -- skin like leather, heavily calloused, grimy hands -- incongruously attired in a worn light flannel suit of collegiate cut, flashy blue sweater, also worn, belted tan topcoat, and cap to match. These clothes, he explained, belonged to his eldest son.

"'That's all we've got now. We take turns wearing 'em.'"

The Hickok book is particularly valuable because of the frequent comparisons now made between the Great Depression and 1981. While there continue to be terrible pockets of poverty in the United States, this is not a nation with bread lines and Hoovervilles. Nevertheless, her work has profound meaning for it does offer the needed reminder in this era of Social Darwinism that there are real people who are "ill-housed, ill-clad, ill-nourished."

If Alice Roosevelt Longworth had ever met Lorena Hickok, she probably would have insulted her for personal as well as political reasons. And because she would have done it with provocative originality, even altruists might have appreciated it. As seen in Michael Teauge's "Mrs. L: Conversations With Alice Roosevelt Longworth," Mrs. Longworth had neither the patience nor the time for what she would have perceived as excessive earnestness on behalf of the disadvantaged. As has become well known, the daughter of Theodore Roosevelt had no great affection for the New Deal side of the FDR era.

That's a strike against her, but the woman knew how to live; how "to call 'em as she saw 'em," and that quality is so rare that one has to have some gratitude for her style:

"The Kennedys reminded me of all the Irish who came over in the 1840s . . . they were all those marvelous-looking kitchen maids and policemen."

"It was rather amusing to see how Mamie [Eisenhower] was held up as this Exhibition Mother-in-law thing, in Nixon's time, when you think how Eisenhower did his best to dump Dick Nixon when he was Vice-President."

"Now where I live it is called a 'mansion' (horrid word) and shown to tourists as some kind of dodo's antediluvian lair."

"Most of my friends are either dead or barely tottering over the Hindu Kush with a Smithsonian tour."

It is shame that we cannot enjoy her observations on our actor-president.

"The Roosevelts: A Family in Turmoil," by Lillian Rogers Parks and Frances Spatz Leighton, has neither the compassionate tone of Lorena Hickok nor the wit of Alice Roosevelt Longworth. Instead, it has all the style of Leighton's other works, which include "Fishbait," "My Life With Jacqueline Kennedy," "Drunk Before Noon" and, in case you missed it, "The Sweetest Little Club in the World: The Memoirs of Louis Hurst, Senate Restaurateur."

The present work goes over the old ground of the personal problems of FDR, Eleanor Roosevelt and their children. It offers no insights into any of these people, albeit one gets a pretty good impression of the mentality of the authors.

In a breathless tone, it tells how FDR had an affair with Lucy Mercer and how Eleanor and her mother-in-law did not get along. This is old-hat stuff. The shame of it is that Lillian Rogers Parks, who was a maid at the White House for decades, does seem like an extremely nice woman. She makes many kind remarks about dead, inconspicuous people, and such a lack of self-service in a memoir is refreshing. Parks is not a bitter "peek-and-tell" lady. One is left with the impression that this is a case where a professional "as told to" writer and a publisher saw an opportunity and seized upon it in the hope that the public's taste was sufficiently poor.