THE TAX NEGOTIATIONS between President Reagan and the House Democrats appear to have collapsed again. The Democrats are prepared to cooperate, reluctantly, in the budget reductions. Reasonable people can agree -- and most of them do, in fact, agree -- that a government can slide into slovenly habits of spending that need to be constrained. But the Reagan tax bill drives the basic philosophical difference much harder. Unlike the Reagan budget, the tax bill presses explicitly the view of government as a corrupting influence on the national morality. For the Democrats, that's too much. These are tough times, incidentially, for the political theorists who have been saying for years that the American system always pulls toward the center and tries to step around the fundamental collisions in values.

Every administration has its own vision of great figures and great successes of the past on which to draw for comfort and inspiration. The Reagan administration frequently refers to the Eisenhower presidency, particularly in matters of style, and, selectively, to the Roosevelt presidency. On the large questions of economics -- which it sees as metaphors for morality -- there are strong hints of Calvin Coolidge.

Mr. Coolidge is much underrated as a model to his successors. He did little or nothing to destroy American initiative with onerous taxation.He did less to entangle enterprise in unnecessary regulation -- or any other kind of regulation. He did nothing to undermine the national character with public spending. There is hardly any area of policy in which you cannot say that Mr. Coolidge rigorously adhered to the firm principle of doing as little as possible.

The savings rate is merely a numerical measure of the national habit of self-reliance. The propensity to invest is another way of describing traditional American get-up-and-go. Too high a tax rate undermines not only economic performance but also the nation's ethical sense. Prosperity is its own reward.

The current secretary of the Treasury, Donald Regan, has taken to quoting not President Coolidge, but more appropriately his secretary of the Treasury. Andrew Mellon has been remembered best, and most warmly, in Washington by the very large numbers of people who visit his great museum and the wealth of paintings in it. Mr. Regan is at work restoring the Mellon reputation as an economic philospher. "If the spirit of business adventure is killed, this country will cease to hold the foremost position in the world," Mr. Regan quoted in a speech last month.That line, he said, came from a 1924 Mellon book on taxation. Mr. Regan then added his own thought -- that the present administration offers Americans "the last chance to restore individual initiative."

The Reagan administration's tax cut is, at bottom, not economics but a prescription to restore the country's moral fiber. President Coolidge would have understood -- although he would have said nothing.