THE NATURE OF MASS POVERTY, by John Kenneth Galbraigh (Harvard, $8.95). Also ANNALS OF AN ABIDING LIBERAL (Houghton Mifflin, $12.95). The first presents a thoughtful, iconoclastic view, and Galbraith's central point on the systemic nature of mass poverty makes it an excellent first word on the subject. The second title is a collection of essays and bood reviews on topics ranging from Watergate to Adam Smith, which again illustrate Galbraith's wit, urbanity and his opinionated expertise. TO SET THE RECORD STRAIGHT; The Breakin, the Tapes, the Conspirators, the Pardon, by John J. Sirica (Norton, $15). The Watergate judge offers his own thoughts and recollections of the unprecedented proceedings which went on in his courtroom. Speaking clearly, without too much legal jardon, Sirica gives us a strong and revealing book about the fall of Nixon. SIDESHOW: Kissinger, Nixon and the Destruction of Cambodia, by William Shawcross (Simon and Schuster, $13.95). This study, with its abundance of damning facts enhanced by vivid, descriptive powers, should not be required reading for those interested not only in a Southeast Asian crisis and tragedy, but in the functioning of American diplomatic and peace-keeping machinery. THE POWERS THAT BE, by David Halberstam (Random House, $15). The author of The best and the Brightest has proven himself a consumate master of the run-on sentence and the overstuffed descriptive phrase; lovers of careful prose will have to resign themselves to putting up or shutting up -- that is, if they also are media-freakish enough to want to immerse themselves in a warm waterfall of colorful data about the personalities behind Time, Inc., CBS, The Los Angeles Times and The Washington Post . SENATOR, by Elizabeth Drew (Simon and Schuster, $8.95). Drew, The New Yorker's Washington correspondent, is able to entertain while being relentlessly informative. Here, following the daily routing of Senator John Culver (D. -- Iowa), she skillfully shows the demands and tedium of Senate life. PROGRESS FOR A SMALL PLANET, by Barbara Ward (Norton, $13.95). An unfashionable optimistic book by an economist whose own intelligence and integrity creates in her the firm belief that humankind is indeed capable of solving those problems which threaten its survival. THE MAN WHO KEPT THE SECRETS: Richard Helms and CIA, by Thomas Powers (knopf, $12.95). Only incidentally about Helms, this detailed study masterfully portrays the agency, its managers and their relationships to the adminstration they served. OUR DAY AND GENERATION: The Words of Edward M. Kennedy, edited by Henry Steele Commager. With a foreward by Archilbald MacLeish. (Simonk and Schuster, $12.95). Senator Kennedy's eloqquence is a moot point these days, although no one has ever denied that, supplied with a text, he is na immensely effective public speaker. In this careful selection of excerpts from the senator's speeches, the words roll by the equally carefully chosen photographs like the credits on a movie. The overall impression is of a campaign-year greeting card; yet even cynics will come across passages (and pictures) which move them.