Whatever else he may be, Ronald Reagan is no trimmer. With no disrespect, he reminds you of Horton the Elephant in Dr. Seuss's children's classic, of whom it was written: "He meant what he said. And he said what he meant. And an elephant's faithful 100 percent."

This president is dead in earnest about the basic tenets of the conservative philosophy he has described in thousands of speeches in the last quarter-century. As his biographer, Lou Cannon, pointed out in The Post, key phrases of Reagan's first State of the Union Address were lifted whole from speeches 20 years old.

Reagan's tenacity is both the envy and despair of other politicians. They understand that it is his unyielding advocacy of a particular philosophy that has given him the hard-core support that has sustained his career at the top levels of American politics for 16 years. And they know he is tough to budge from those beliefs no matter how much at odds they may be with the realities of the world.

For much of his political life, Reagan was delivering a message that was anything but popular. He was railing against the dangers of big government when Lyndon Johnson was assembling the Great Society programs and Richard Nixon was expanding on them.

It was 1975 when Reagan first proposed the massive transfer of programs to the states. The idea boomeranged. President Ford and his backers portrayed it as a plan that would boost local taxes, and used it to beat Reagan in the lead-off 1976 primary in tax-conscious New Hampshire.

Most politicians would have buried any idea that, arguably, cost them nomination to the presidency. But Reagan is not most politicians, and so the fiasco of 1976 becomes the keystone of 1982.

The toughnes of the president is perhaps the most underestimated of his qualities. His manner seems relaxed, and his mind seems open to persuasion. Anyone who meets him is apt to describe him as a "good listener." But time and again, Reagan reverts to those essential beliefs that were forged in the distant days when he was converted from a New Deal Democrat to an apostle of conservatism. He insists on putting his own principles into practice.

His own senior staff members seemed stunned that they were not able to persuade him to raise taxes to reduce the looming deficits. And many of them seem equally surprised that, in a time when the immediate economic problems look overwhelming, the president would push something as complex and controversial as his "turnback" program onto the legislative and political bargaining table.

In both cases, there are plenty of well-informed people, many of them members of the president's own party, who are convinced that his policies are flat-out wrong. The top Republicans on the tax-writing and budget committees of Congress are almost unanimous in the view that it is essential to recapture some of the revenues so heedlessly squandered in last year's orgy of tax-cutting. And in Congress and the state capitols, some of the best-informed Republican students of the federal system see gaping holes in Reagan's version of the "turnback" program.

Those questions will now be tested in the political arena, if they are not overwhelmed by real-world economic problems. The quick political reaction that Reagan's federalism plan is simply a diversion from those economic woes is as unfair as it is unfounded. The issue of rationalizing functions among levels of government is fundamental to the future health of this society and all of its citizens.

But even Reagan's pollster, Richard Wirthlin, concedes that "at some point, people are going to have to see some improvement in the economy" for Reagan to maintain the legitimacy of his leadership. "Hope has been extended," Wirthlin said, "but at some point, it has to be justified, to make it all worth the candle."

The risk for Reagan and the Republicans is that if that moment does not arrive this year, his steadfastness will be seen simply as stubbornness or obliviousness to reality.

But if that is the potential risk, there is an immediate reward for Reagan's course of conduct. By sticking to his guns, he has forced his issues to the top of the national agenda. It has taken time, but the debate in Washington is now on the ground Reagan has chosen: about the costs of big government, high taxes and the federal superstructure.

That is not what Congress and the country would be chewing about this winter, were not Reagan the stubborn and principled character he is: the Horton the Elephant of American politics.