SEN. EDWARD KENNEDY spoke a major contemporary heresy in his announcement of candidacy in Boston last Wednesday. "I was taught long ago that politics in a noble occupation," he said, "that public service is among the most honorable of professions." It's enough to make you wonder whether Gov. Jerry Brown of California is right when he insists that Mr. Kennedy belongs to, and in, an earlier era.

Sen. Howard Baker, too, has been expressing this heresy, provocatively claiming that he is proud of his maligned political calling. Contrast the two men's revisionism with the moral outrage of Richard M. Nixon, who, in April 1973, told us a thing or two about political campaigns and the "inexcusable campaign tactics that have been too often practiced." Mr. Nixon characteristically did not pull any punches in giving the lowdown about the profession he had graced for most of his life when he revealed that "both of our great parties have been guilty of such tactics in the past." Imagine.

President Carter, who ran successfully against the excesses and crimes of the Nixon years, has never been (rhetorically) very high on either politics or government. In fact, during the 1976 campaign, he repeatedly offered as a credential that he had never been listed in the white pages of the District of Columbia telephone book. That was campaign shorthand for: Jimmy Carter had not been corrupted by hanging around with all those polictical and governmental types. He was one of "us," not one of "them."

But the "us" and "them" scheme is weak. This nation's most effective presidents -- Jackson, Lincoln, Wilson, the two Roosevelts -- were pround and partisan politicians. They did not view politics or public services as either a joyless task or as a gloomy obligation. Nor have any of Mr. Nixon's party colleagues -- Sen. Goldwater, Gov. Rockefeller, Gov. Romney, Gov. Reagan, President Ford, President Eisenhower -- viewed campaigning as something requiring emergency powers and suspension of the Bill of Rights.

Politics, as practiced effectively and enthusiastically by masters, can be an important, interesting and honorable profession. Important, and interesting, because in the last analysis the saving of our public schools, the safety of our public streets and the sensibleness of our public debate are all political questions. Honorable because if politics -- both the practice and the profession -- are permanently discredited, how is a nation as diverse as ours supposed to resolve the urgent questions of competing interests? By numbers? By money? By muscle? Or by the compromise and conciliation and eventual cohesion that gifted politicians are necessary to produce?

Politics is not yet an endangered species, as we saw (in spite of his protestation) during Mr. Carter's "loaves and fishes" performance in Florida during his recent exhibition game against Mr. Kennedy. That is the reality. But how long can any society tell its young people that interest in a profession offers conclusive proof of moral leprosy before that judgment becomes self-fulfilling?