There are three ways of dealing with America's social problems: the liberal approach, the conservative approach and the Reagan approach.

The liberal approach holds that people with problems need help, and that it is a proper function of government to furnish that help. The conservative belief is that since government, whatever its good intentions, is likely to make problems worse, the most helpful thing it can do is get out of the way.

The Reagan approach says: Problem? What problem?

For more than four years now, we've been arguing over how best to solve problems: more federal aid for education or more choice of schools; more welfare with more dignity, or more work-or-starve sternness; more attention to root causes, or more penalties for inappropriate behavior.

We've accused each other of mush- minded liberalism or stone-hearted conservatism, of being too wedded to orthodoxies or else too easy marks for anything that begins with "neo." But each of us has assumed that the other was at least interested in solving the problem.

That may have been what the rest of us believed, but not President Reagan.

Remember when Reagan first proposed massive tax cuts, based, he said, on "supply-side" principles? Those who disagreed with his plan argued that his economic assumptions were wrong, contended that it was impossible to increase defense spending while massively cutting taxes without running up a dangerous deficit and finally were left to hope against hope that he just might pull it off. (At least he brought inflation under control, said some of the whistlers-past-the-graveyard.)

In any case, the arguments were over whether the supply-side approach could possibly work. Now comes the word that Reagan never expected it to work; that he had something entirely different in mind.

Sen. Daniel Patrick Moynihan (D- N.Y.) says the departing budget director, David Stockman, told him some time ago that Reagan never believed in supply-side economics and knew the tax cuts would result in serious budget deficits.

So why did he advocate the tax cuts? "The plan," Moynihan said he was told, "was to have a strategic deficit that would give you an argument for cutting back the programs that weren't desired."

That is, while the rest of us were arguing over the efficacy of one approach or another, Reagan had decided that there were certain programs the government shouldn't be involved in, not because they didn't work but because they weren't, in his view, the government's business. The plan was not to solve problems but to reduce revenues to the point where even liberals could not reasonably look to government for solutions.

Reagan, according to the Moynihan account (which Stockman hasn't denied), simply never cared about solving the social problems. By this reading, the "safety nets" for the "truly needy" were, like the presidential calls for a resurgence of voluntarism, simply devices calculated to keep us from seeing the truth: that the president's principal goal was not to make things better for the society but to shrink the size of government.

And the truth is, he has accomplished that goal. Hardly any member of Congress, no matter how liberal, is calling for any major new spending programs; the deficit, you know. America's problems haven't shrunk; but thanks to the Reagan trickery, government's ability to address those problems has shrunk.

The question is, now that congressional liberals understand the nature of the trick, what will they -- what can they -- do about it?