Never read a book that is not a year old. - Ralph Waldo Emerson
Lyndon Baines Johnson, our 36th President, was wealthy, secretive, intensely ambitious, and unquestionably one of the great politicians of our time. Robert A. Caro's The Path to Power (New York: Vintage, $9.95.) is the first of three volumes about LBJ's life, and the detail, insight, and narrative flow of this massive book make it obvious why Caro's book won the National Book Critics Circle award for nonfiction in 1982. ''The Path to Power'' starts with Johnson family history and takes LBJ up to 1941 when, at age 33, he was already wielding enormous influence in the House of Representatives. Great biography.
Dobrica Cosic's (pronounced Doe-breech-ah Chose-itch) tetralogy Into the Battle, A Time of Death, Reach to Eternity, and South to Destiny (Harcourt, Brace Jovanovich, $7.95 each) on World War I as seen through Serbian eyes is also political and massive - 1,400-plus pages in four volumes. Well translated by Muriel Heppell, it begins with the assassination of Archduke Franz Ferdinand in Sarejevo in 1914 in ''Into the Battle,'' and subsequent volumes - ''A Time of Death,'' ''Reach to Eternity,'' and ''South to Destiny'' - take us through the great war and demonstrate the skills of one of Yugoslavia's best and best-known novelists.
Bernard Kalb and Marvin Kalb are both National Broadcasting Company (NBC) correspondents, and their many years of politics-watching serve them well in The Last Ambassador (Berkley Books, $3.50), a novel about the suspenseful last days in Saigon for Americans in 1975. Lots of inside-seeming stuff.
At first glance, Quintessence (Crown, $12.95), by Betty Cornfeld and Owen Edwards looks like a frivolous book. It's not, though, despite its often arch tone, because Betty Cornfeld and Owen Edwards show and tell us about cultural artifacts that are the essence of their kind. Things that ''have it'' include Ivory soap, Bass Weejuns, Barnum's Animal Crackers, Jockey Briefs, Crayola crayons, M&Ms, Hershey's Chocolate Kisses - you get the idea. Popular culture very cleverly done.
For sheer entertainment of the hard-boiled criminal variety, it's hard to beat Elmore Leonard. Now available are two of his novels from the mid-1970s - Unknown Man No. 89 and 52 Pick-up (Avon, $2.95 each) - which feature, in classic Leonard fashion, engaging ''underdogs'' and exceptional dialogue. If either of these books hook you, then look for ''City Primeval,'' ''Cat Chaser,'' and ''Split Images,'' more vintage Leonard.
People have always been fascinated by photographs of faraway places, and never more so than during the mid-19th century when photography was young. Samuel Bourne: Images of India (The Friends of Photography, PO Box 500, Carmel, Calif. 93921, $16) contains 26 very nicely reproduced plates of Bourne's work in India between 1864 and 1869 and also a fine biographical essay on the English photographer by Arthur Ollman.
In Ivan Doig's The Sea Runners (Penguin, $4.95), the year is 1853, the setting the Pacific Northwest, and the subject the escape of four Swedish indentured laborers from a work camp in New Archangel, Alaska. They plan to travel 1,000 miles in a 20-foot canoe. What stands out about Doig's first novel is the perfect sense of place it projects, a talent also demonstrated by Doig in his nonfiction works, ''This House of Sky'' and ''Winter Brothers.''
The land itself is the subject of Chet Raymo's The Crust of Our Earth (Prentice--Hall, $12.95). This guide to the new geology, which centers on plate tectonics, contains 60 mini-essays, each of which has instructive illustrations and/or maps, and it enables anyone with an interest to understand recent revolutionary developments in earth science. A complicated subject brought into sharp focus.
Melvin Konner is interested in the nature of human nature, interested in probing biological reasons for why we are the way we are, why we feel rage, joy, fear, love, and grief. In The Tangled Wing (Harper Colophon, $8.95) he tells us what he knows about the above, and also about behavioral change and future prospects for a deeper understanding of human behavior. Konner is a biological anthropologist and a very learned man. He is up on developments in medical and social sciences as well, and the result is a humane, readable, and impressive book.
The Early Stories of Willa Cather (Dodd, Mead, $5.95) selected and with commentary by Mildred Bennett, are early indeed. All 19 were published before 1901, long before such fine novels as ''My Antonia'' and ''Death Comes to the Archbishop.'' While seeds of her later work are visible in these stories, the stories themselves are interrupted by Bennett's many notes, interpolated, alas, within the text. More an edition for study than casual reading.
Stephen King not only writes horror-filled books that are then faithfully turned into films, but he is also a student of the genre that has brought him fame. Danse Macabre (Berkley Publishing, New York, $3.95), a best seller, is King's odyssey through the fantastic and scary as it came to him in films, books , radio, and television.
No, it's really not too early to think (or dream) about gardens, and therefore not the wrong time of year for Eleanor Perenyi's Green Thoughts (Vintage, $5.95). Herbs, evergreens, perennials, earthworms, compost, roses, wildflowers, toads, and even magic - Perenyi's subjects are anything garden-related, but this is not a how-to book. It is a personal and somewhat quirky but beautifully written book of one writer's thoughts on growing. An annotated list of catalogs is at the book's end.
Want to know Stephen P. Barry's story? Probably not, unless you're aware that he was Prince Charles's valet for 12 years. Royal Service (Avon, $3.50) is where Barry tells us the ''inside story,'' and it proves that a man can be a hero to his valet.
Joseph Wambaugh is a veteran of the best-seller lists, and his latest, The Delta Star (Bantam, $3.95), is yet another of his fine novels about neurotic cops and eccentric criminals.