MEMOIRS of public figures always are suspect, and properly so. Autobiography itself is, by its nature, self-serving and a massive exercise in puffing up an already inflated ego.Jean-Jacques Rousseau, as Henry Adams recalled, could begin his famous Confessions with a passionate claim to have exposed his inner self: "I have shown myself as I was; contemptible and vile when I was so; good, generous, sublime when I was so; I have unveiled my interior such as Thou thyself hast seen it, Eternal Father!" But surely even readers in that far more gullible time knew what Rousseau had to say about himself was not always so.

When a politician offers what purports to be the truth about himself and his times, readers have even more reason to beware. Adding these necessary qualifiers, though, in no way detracts from the value of these reminiscences of Jacob Javits. He is one of then most admirable politicans America has produced, and his story deserves attention -- particularly today when the concept of public service has been so badly eroded and the mere mention of the word politican brings a cynical curl to the lips. Perhaps next to those of us in the press, who also have a rather highly inflated view of our importance, politicans are the object of most public scorn these days.

Let it be said that you'll not find a light touch in these pages. Javits takes himself entirely seriously and without a welcoming air of occasional wryness or self-depreciation. Nor is his story unique; its very familiarity is one reason for its significance now. His is the classic tale of the immigrant offspring, the son of the janitor toiling in New york's teeming Jewish ghettos at the turn of the century, who through pluck, perserverance, and talent battles his way out of the slums and into success. Fame and fortune and public recognition are his lot -- Horatio Alger lives.

We all have heard that one all our lives, and continue to hear it extolled in this Reagan era, the hallmark of which appears to be a return to the laissez-faire, free-booting, no-government-and-no-regulations-are-necessary spirit that characterized the Calvin Coolidge presidency. Javits' life and career remind us why those kinds of attitudes were rejected, and how the role of government became so great in so many aspects of American society. He came out of the slums filled with a burning indignation at the social, racial, religious, economic, and political injustice and intolerance he witnessed. To a rare degree his public career has been a consistent outgrowth of those early experiences.

In 24 years as a United States senator (the longest anyone ever served from the state of New York) and in three terms as a congressman, Javits was at the center of the major struggles for civil rights and civil liberties, for progressive legislation in everything from public housing to health in the post-World War II era. he was one politician who made a difference.

Javits was a Republican, of the progressive Theordore Roosevelt, Fiorello La Guardia stripe, and as such a vanishing breed in American politics. His conception of the role of government differs markedly from a majority of the Republicans who now conrol the Senate in which he served so long. Like many of his time and place, Javits had been attracted to socialism during his youth, and then changed. He and his older brother, Ben, the single greatest influence in his life, and the most interesting relationship he explores in the book, debated political and social questions intently and in time drew apart philosophically.

"Eventually," he writes, "Ben's beliefs led him to a position that was very close to corporate statism, the original foundation of Italian Fascism, in which society is divided into workers, employers, and technicians. fThe essence of his system was his faith that the managers of business would do what was in the public interest. While I shared his view that the functioning of a corporation could invalidate much of socialist theory, I never shared his faith that business managers, standing alone could be entrusted to operate business in the public interest. I believed that the will of the people could be best expressed through government and that government-business collaboration could encourage business to perform in the public interest. Although I felt that we could rely upon the U.S. business system to run the U.S. economy, I did not feel that we could entrust the economic well-being of the American people solely to the multitudinous transactons of the marketplace."

Try that one out around the Reagan Republican White House and see how far you get.

For all his astuteness and political skill, Javits fell into a common political trap. He made one race too many. Last year, at the age of 76, ill and visibly less energetic, on his 10th try for elective office, Javits suffered his first, and final, political defeat. Days before he lost, he made a sentimental -- and sad -- return to the Lower East neighborhood in which he was born. "As I shook hands with so many people there on the street corner where it all began for me," he writes, "I realized that they knew what I was and that they knew what I had accomplished for them and for all of us, and I saw that one defeat meant little on the long road I have traveled."

If he seemed to have an unnecessary need for reassurnace, perhaps that, too, is part of the essential makeup of the public man who seeks public approval and acclaim. Whatever, you finish these pages wishing we had more like him.