Of all the animals in our political zoo, none has been more scorned than the creatures that call themselves "moderate Republicans." In the days of Democratic dominance, true conservatives derided them as "me-tooers." Since 1964, they have been predictable losers in Republican conventions. In Detroit last summer, they were by-standers at the Reagan coronation, so impotent they were not even good targets for conservative jibes.

One highly credentialed moderate, Sen. Howard H. Baker Jr. of Tennessee, saw his presidential bid collapse early in the year. Another, Rep. John B. Anderson of Illinois, was routed, so thoroughly that he left the GOP for a foredoomed independent candidacy.

Having undergone so many humiliations, these creatures became masters of self-depreciation. When they chose a label for themselves in this Congress, it was "gypsy moths." "We moderates," said Sen. John C. Danforth of Missouri, "are such vanilla characters, we put you to sleep."

But as they say, what goes around, comes around. And the moderate Republicans are sensing accurately these days -- and asserting plainly -- that they have a vital role to play in the future of the Reagan administration and the Republican Party.

The frantic negotiations that led to formulation of the latest round of budget cuts were different in one respect from those of last spring. This time, the goal of the White House operatives -- a goal they did not reach -- was to satisfy the gypsy moths, not the Southern Democratic boll weevils, on the equity of the president's proposals.

They understood that Democratic resistance to Reagan's austerity measures was increasing, and their only hope of success lay in holding Republican ranks intact -- including the two dozen House members and the handful of senators who consider themselves political moderates.

By coincidence, the week that ended with Ronald Reagan's speech to the nation began with a massively less publicized "moderate manifesto" by Rep. Jim Leach of Iowa, a 38-year-old third-termer who is characteristic of the breed in his combination of brains, good manners and innocuousness.

The occasion of Leach's adress was his acceptance of the chairmanship of the Ripon Society, an academically oriented group of moderate Republicans formed back in the Kennedy years and now boasting a national membership of 2,500 hardy souls.

The best recommendations for the moderate Republicans have always been the quality of their ideas and the quality of their people. Leach embodies that tradition. A foreign service officer who resigned on principle to protest Richard Nixon's "Saturday Night Massacre", he made his manifesto an exceptionally clear statement of the moderates' principles and policies.

In barest outline, he called on the Reagan administration to: balance the arms buildup with an equally serious bid for arms control; recognize that military intervention cannot be our basic approach to Third World disputes; reassert American concern for human rights; limit further tax benefits to the energy industry and prevent further cuts in education and basic research; fight monopoly distortions of free enterprise with vigorous antitrust enforcement; protect the historic Republican commitment to environmentalism against the "aberrations" of James Watt; reassert Republicans' commitment to civil rights and equal justice and reject the social-issue conservatism of the New Right.

If all this sounds to some people like asking Ronald Reagan to stop being himself, Leach can not only invoke a pre-Reagan Republican tradition, but explain why he supports the main goals of the Reagan administration and hopes for its success. "We have a major stake," he said, "in making the Reagan administration the best possible administration, because he has set such a positive direction for conservatism that if he can avoid the extremes, he can establish a generation of Republican opportunity."

Of all the elements of Reagan Republicanism, moderates probably feel most comfortable with the emphasis on decentralization of government. As Leach pointed out, "The real divisions today in the Republican Party are not between liberals, moderates and conservatives; they are between pragmatists and ideologues. . . . It is local government where pragmatists have always dominated."

In a quiet way, Leach's speech was a timely reminder that the moderates are still around -- not just in Congress but in state capitols from Iowa to Pennsylvania and Vermont, where they will play a major role in determining the GOP's fate in the 1982 and 1984 elections.

Leach got invitations to discuss his views on CBS, public television and the Cable News Network -- and a request to stop by the office of Vice President Bush. Just want to be sure there are open channels of communication to the administration, Bush said. The moderates are making their point.