The Decline and Fall of the British Aristocracy, by David Cannadine (Yale, $35). A century ago the British aristocracy was secure in the possession of broad acres, rent rolls and ancient titles. Common people followed the doings of the toffs in the newspapers, and a ducal wedding was a national occasion. But nowadays the aristocracy lives on the margin of British society, except for the odd throwback, like Sir Alec Douglas-Home or Lord Carrington. What did the grandees in? Confiscatory taxation, the breakup of the great estates, two world wars and the erosion of the traditional system of titles -- Lloyd George, for one, systematically sold titles to political contributors. And horror of horrors!: Fox hunting is now largely a middle-class affair. This highly entertaining social history, full of fascinating anecdotal material, by a young British historian now teaching at Columbia University is the last word on the subject.

Agatha Christie: The Woman and Her Mysteries, by Gillian Gill (Free Press, $22.50). Dame Agatha Christie could turn out fiendishly clever mysteries in the same way that Ethel Merman could belt out showtunes and Stan Musial hit line drives -- all three were naturals whose performances could be admired but hardly emulated. Christie was no literary light -- her creaking prose was one of the forces that pushed Edmund Wilson into the anti-mystery camp ("Who Cares Who Killed Roger Ackroyd?" he fulminated in a famous essay, referring, of course, to Christie's most notoriously twisty novel). But the author of this biography makes a good case for her as at least an interesting writer on the strength of "her many loves -- of husbands and books and ancient cultures, of architecture and music and landscapes, of tennis and bridge and crossword puzzles, of interior decoration, and food and pets."

The Audubon Ark: A History of the National Audubon Society, by Frank Graham, Jr. (Knopf, $29.95). As the Sierra Club has been identified with John Muir's prose and the Wilderness Society with Ansel Adams's photographs, the National Audubon Society is closely linked with Roger Tory Peterson's marvelous bird paintings and guides. Birds, indeed, have always been National Audubon's preoccupation, as they were of its namesake, the indefatigable ornithologist and illustrator John James Audubon. As the writer of this authorized but candid history points out, "the Society's greatest treasure" lies in its own non-governmental system of wildlife refuges, much of it prime avian habitat.

Circus Dreams: The Making of a Circus Artist, by Kathleen Cushman and Montana Miller with photographs by Michael Carroll (Little, Brown, $15.95). Like the Foreign Legion, the high-kicking chorus line and the roster of astronauts, the circus is the subject of countless childhood joining-up dreams. Montana Miller didn't just dream of performing under the big top. She turned down a scholarship to Amherst College, strapped on a funny nose, moved to France, and tried out for trapeze training at the National Center for Circus Arts in Chalons-sur-Marne. She seems to have had more trouble learning French and performing in acting class than swinging through the air, but the book ends on a note of triumph, with Montana earning her spurs as a daring young woman by subbing for an indisposed "female flyer" in a Mexican circus on European tour.

The Last Modern: A Life of Herbert Read, by James King (St. Martin's, $35). Critic of art and literature, poet, novelist, publisher, Herbert Read (1893-1968) was one of those Renaissance Englishmen who used to come down the pike with daunting regularity. He was also a pacifist and anti-establishment scold, and so his biographer gives an arch twist to the beginning of the chapter explaining how he became Sir Herbert: "Nineteen fifty-two came to an end with a piece of disturbing news: a letter . . . from the Palace offering Read a knighthood for 'services to literature.' " Eventually he managed to swallow the honor, in large part because his wife wanted him to, but not without telling friends they might as well start lumping him in the same category with "jockeys, actors, music-hall comedians."

Productivity: The American Advantage, by L. William Seidman and Steven L. Skancke (Simon & Schuster, $18.95). Here is an insider's report by a contemporary hero. L. William Seidman, the man winning acclaim for the seemingly thankless task of managing the S & L crisis for the federal government, has co-authored an advisory for American corporations determined to regain their competitive edge. Fifty exemplary outfits are singled out for one or more aspects of their operations -- from giant electronics firm Hewlett-Packard (for its quality-control program) to, of all organizations, the New York City Department of Sanitation (for its rapprochement between management and labor).

The Growth Experiment: How the New Tax Policy is Transforming the U.S. Economy, by Lawrence Lindsey (Basic Books, $21.95). Here is a bold assault on up-to-the-minute conventional wisdom: Contrary to the assumptions that seem to be guiding those acting to slash the federal deficit, tax-cuts for the wealthy have been part of the solution, the author contends, not the problem. Indeed, far from raising taxes, he would extend to the middle class the cuts for the rich that have proved so controversial over the last few years. That the author was a member of the Reagan administration and currently works for George Bush may give his arguments a partisan tinge; on the other hand, his position as a Harvard economics professor (on leave) lends them a scholarly stamp.