THE POLITICIAN'S "book" is as durable as rubber chicken. Stay in Congress long enough, and one will be slung round your neck by a publisher under the misapprehension that yur views are your own, or in hpes that one day you may be president, or arrested, or both.

Why anyone wuld pay for speeches and other Rotarian fare sandwiched between high-priced boards remains a greater mystery than whither the Democratic Party, or why Eugene McCarthy endorsed Ronald Reagan, and yet they appear even in the worst of seasons. If anything good can be said for the congressional franking privilege, it is that it should protect us from such offerings. Members of Congress already have free access to the mails; they don't deserve the library shelves as well.

There are no doubt rare examples of insightful memoir and commentary by politicians, although none comes immediately to mind. Most politicians' books, like these, seek to advance the author's career, or his memory, at the expense of candor and that other difficult ingredient, art.

Eugene McCarthy should be an exception to the rule, being both a fromer senator and that most celebated of alternative creatures, a poet. But Complexities and Contraries -whatever those may be -reads like what it is: old newspaper columns, published in The Washington Star in 1977 and 1978, that are dated beyond their years. The subtitle, "Essays of Mild Discontent," suggests a laconic senior statesman wryly commenting upon the foibles of his successors, a curious role for McCarthy, whose politics have been anything but consistent. Mild discontent, however mellow, seems equally inappropriate to the age of second strikes and 10 percent unemployment.

In fact, the pieces arre peevish and self-serving. McCarthy devotes one to the defense of an embrace between himself and Henry Kissinger, lest McCarthy appear to be curting power. "The fact is that I have a reputation of not being very demonstrative." Apparently Kissinger embraced him . In a piece on the neutron bomb, McCarthy offers an example of his wit: "We have had the Bowie knife, the Patton tank, the Sherman tank. . .We culd have called the atomic bomb the 'Harry,' and the hydrogen bomb the 'Ike.' Now we have the 'Jimmy Carter cookie cutter.'

McCarthy seems to think his public opposition to the vietnam war in 1968, and his reputed scholarship, absolve him of the need to reveal anything of himself, or to rewrite. The articles are heavy with quoted peotry, some of it McCarthy's own, and historical facts deposited like dumplings. He does not bestir himself to discuss his won ambitions or the country's, or why he espoused for president a bellicose Californian considerably less interested in poetry than in fenceposts.

To her credit, Rep. Millicent Fenwick (R-N.J.) states honestly in the preface, "This is mostly a book of letters to the people of the Fifth district of New Jersey who sent me down to Congress." Her constituents may be more interested in her musings on human incompatibility and the greatness of the House of REepresentatives than the rest of us will be. She doesn't pretend to entertain or instruct; rarely has so much been endoresed or deplored in so few pages. She's for common sense, employment and "eternal verities," and against government subsidy and a sensational press. She's also in favor of occupying a seat in the United States Senate.

Rep. Paul Simon (D-Ill.), by contrast, has a message: the Democratic Party has a future, and it closely resembles the past. "Those who see a sweeping conservative trend outside the South have not studied the votes carefully," he writes of the 1980 election. "Ideology appears to have been a secondary consideration for most voters."

This bundle of liberal encomiums reads suspiciously like testimonials stitched together by many busy hands in that great sweatshop on the hill; the seams show. "Where do we go from here," he asks in the introduction, and then pedals backward through a familiar agenda for creating jobs, improving the economy, education, government services, the cities, and defense through increased public spending.

Simon prefers the Q&A format -that uncontentious fellow in the audience who tosses up rhetorical softballs for Simon to clobber into the bleachers. He quotes many people, from Plutarch to himself, and gives credit where it's due: "Let me give you an ilustration of something I did well." (The discovery that many banks in southern Illinois had invested in New York City bonds and therefore would have been harmed by the city's bankruptcy.) Simnon hopes for "greater compassion, for improved productivity, and for enrichment of the quality of life in every dimension."

So do we all. But those sentiments do not make compelling reading, just as public statements and expressions of mild discontent do not make books. What these slim collections lack is the simple, passionate need to say something, and the skill to say it well. They contribute to the skepticism of what's left of the reading public, and the penury of real writers.