Never read a book that is not a year old. - Ralph Waldo Emerson
William Least Heat Moon's Blue Highways (Ballantine, New York, $3.95) has moved from the hard- to the soft-cover best-seller list without skipping a beat, and for good reason - it's a terrific book, a deeply personal look at America from the backroad and the back room, a nonfiction picaresque that demonstrates the diversity of this country as few books have.
A good companion piece to ''Blue Highways'' might just be J.J.C. Andrews's The Well-Built Elephant (Congdon & Weed, New York, $16.95). It features restaurants built in the shape of coffeepots and hot dogs, a car wash like a whale, and motels with tepees for rooms. Too many of the photos are black and white, but this is still a fine collection of vernacular American architecture at its most eccentric.
Few people have done more to make science accessible to the general reader than Lewis Thomas, beginning, of course, with ''The Lives of a Cell.'' The Youngest Science (Bantam, New York, $6.95) is Thomas's autobiography, and it shows the development of a doctor in conjunction with the development of modern medicine over the last half century. Thomas is incapable of being anything but interesting.
John McPhee, a staff writer on The New Yorker and quite possibly the best nonfiction writer we have, has been interested in geology recently. First, there was ''Basin & Range,'' and now there is In Suspect Terrain (Farrar, Straus & Giroux, New York, $6.95). Further adventures in the world of plate tectonics, this time featuring a goelogist named Anita Harris, and impeccable prose.
All the books in the ''Past Masters'' series are essentially primers on the work and lives of great cultural figures. Each is roughly 100 pages long, and contains suggestions for further reading. Additions to the series include: The Buddha, by Michael Carrithers; George Eliot, by Rosemary Ashton; William Morris, by Peter Stansky; Tolstoy, by Henry Gifford; Diderot, by Peter France; Proust, by Derwent May; and Muhummad, by Michael Cook (Oxford University Press, New York , $3.95 each).
Leslie Fiedler has been a very squeaky wheel on the wagon of literary criticism for years, a provacateur who announced the death of the novel and who wrote the famous essay ''Come Back to the Raft Ag'in, Huck Honey.'' His latest book, What Was Literature? (Touchstone (Simon & Schuster), New York, $6.95), keeps to his controversial and lively standard.
If you're one of those who likes the outrageous quotation, try No Matter How Thin You Slice It, It's Still Baloney (Quill, New York, $5.95). Jean Arbeiter has assembled a fine assortment of gaffes; they are listed in 24 categories.
The National Security Agency is the United States' most secretive government agency, and James Bamford's The Puzzle Palace (Penguin, New York, $7.95) looks inside many of its closets. Bamford's book is dense and full of acronyms (which are deciphered in a glossary), but all in all, this is an eye-opening look at a most covert institution.
Ted Morgan's Churchill: Young Man in a Hurry (Touchstone, $10.95) is an exceptionally readable biography of the first 41 years of Winston Churchill's life and a practical alternative to the official biography, which now numbers over 4,400 pages. Churchill was a senior minister by his early 30s, and this chronicle leaves him during World War I after his not wholly successful stint as First Lord of the Admiralty.
If you enjoy the adventures of Rumpole of the Bailey, there are three books you should know about. The first two - The First Rumpole Omnibus (Penguin, New York, $7.95) and Rumpole for the Defense (Penguin, $2.95) - contain various of the barrister's cases, while Clinging to the Wreckage (Penguin, $5.95) is an autobiography by Rumpole's creator, John Mortimer, himself an esteemed lawyer, not to mention talented playwright, journalist, and, recently, adapter of ''Brideshead Revisited'' for ''Masterpiece Theatre.''
Last Stands: Notes From Memory (McGraw-Hill, New York, $6.95) is Hilary Masters's autobiography. Masters, the son of Edgar Lee Masters (''The Spoon River Anthology'') and born when his father was 60, lived primarily with his grandparents in the Midwest. Beautifully written, this book reads as if its memories were evoked by a random journey through a family photograph album.
Unlike tall tales, novels do not always improve with age, and the reprinting of long out-of-print works can be disappointing. Happily, this is not the case with the work of E.F. Benson (1867-1940). His comedies of manners are very funny , and the vain airheads who populate his novels are wonderfully drawn, as you will discover when you read Mrs. Ames or Paying Guests (Chatto and Windus, London, $7.95 each), or the first three ''Lucia'' novels, Queen Lucia, Lucia in London, and Miss Map (Perennial (Harper & Row), New York, $3.95 each).
Muriel Spark is one of England's best novelists, the author of more than 25 books, among them ''Memento Mori'' and ''The Prime of Miss Jean Brodie.'' There are now five additions to her work in paper; they are The Comforters, The Bachelors, The Driver's Seat, The Abbess of Crewe, and Territorial Rights (Wideview/Perigee (Putnam), New York, $6.95 each). Spark's characters are often types, her images spare but precise, and the mood somewhat grotesque, but they are nonetheless compelling moral tales.
It's hard to escape the fact that this is an election year, but did you know who's doing the electing? In Why and How Women Will Elect the Next President (Harper & Row, $6.95), Eleanor Smeal tells us the hows and whys of her stated subject. An appendix contains a resource guide to political organizations of interest to women, 53 percent of the eligible voters.