No sooner had President Clinton unveiled his plan to save Social Security than it was savaged as big government run amok.

Republicans are reacting so hysterically precisely because the plan -- a solid proposal surrounded by poll-driven vacuities in his State of the Union address -- is not wild liberalism. Rather, it is fiscal conservatism -- what Republicans used to stand for before they invented supply-side economics -- devoted to progressive ends.

The gist of Mr. Clinton's proposal, remember, is not to spend the budget surplus but to save it. Three-quarters of the budget surplus would go to the Social Security and Medicare trust funds, which would save some of the money directly and use most of it to reduce the national debt. With the Government soaking up less private savings, more would be available for corporate investment. Most economists -- and especially conservative economists -- consider this the best way to boost economic productivity.

Indeed, Republicans do not dispute the conservative merits of debt reduction. Instead, they throw up their hands and moan that it is not realistic.

"Knowing the proclivities of democracy, and the Congress particularly," Representative Bill Archer, chairman of the House Ways and Means Committee, sighed last week, "it's very unlikely that that will happen." But the Republicans, not least Mr. Archer, are the very ones who are insuring it won't happen with their insistence that the surplus go toward tax cuts instead. It is reminiscent of the protection racketeer who sadly warns that the neighborhood is a dangerous place when he's the one who's making it dangerous.

So Republicans aren't arguing against debt reduction on economic grounds. Instead, they say the budget surplus "belongs to the American people." But what does this mean? Mr. Clinton, after all, isn't planning on giving the surplus to foreigners or setting it on fire; he wants to put it toward an end that benefits the American economy as a whole.

The Republicans, by contrast, are making a distributional argument. They want the surplus to reduce income taxes, most of which are paid by the well off. Mr. Clinton's plan, then, is concerned with enlarging the size of the economic pie, while the Republicans are more interested in how to divide it up.

According to conservatives, the most dangerous part of the Clinton proposal is investing a portion the Social Security trust fund in stocks, so that, in the long run, the higher returns help keep the program solvent. As a scholar at the American Enterprise Institute, Kevin Hassett, put it, "If the Government owned all the equities, we wouldn't really be much different than the old Soviet Union." Really? The absence of free elections, the suppression of dissidents, the state-run economy, the furry hats -- all that in one seemingly innocuous accounting shift?

If the fearmongering is working, it's because it seems to make sense at first blush. Having the Government own shares of the private sector is indeed dangerous. But listen to what Mr. Clinton actually proposes to do.

He wants to take a small portion of the budget surplus and turn it over to the Social Security trust fund. The trust fund would give the money to an independent board, whose members would be insulated from political influence the same way members of the Federal Reserve are. They would hire private-sector fund managers to invest the money in passive index funds and forfeit all voting rights on those shares. Could future Congresses change the rules if they wanted to attach strings to the money? Sure, but they could do the same thing to the Federal Reserve -- a far more tempting target.

There may well be some flaws in this proposal that haven't come to light. But conservatives haven't even tried to figure out what these might be, preferring instead to dismiss it out of hand.

It's not hard to figure out why. Conservatives have never warmed to Social Security, particularly the way it redistributes wealth. Republicans thought Social Security reform would give them an opportunity to privatize the system. Their most politically potent argument was that a privatized system would allow individuals to enjoy the higher returns that the stock market historically yields. But if you can get those higher returns without privatizing, as Mr. Clinton suggests, then privatization loses its appeal to all but hard-core conservatives.

Congressional critics are making much of the fact that Alan Greenspan, the chairman of the Federal Reserve, expressed his opposition to putting the trust fund in stocks. But Mr. Greenspan also said using the surplus for debt reduction -- the main element of the Clinton plan -- would be preferable to tax cuts. In truth, there is no reason to give special deference to Mr. Greenspan's views on budgets and taxes. He is responsible for monetary policy, on which we quite properly hang on his every word, but on other matters his thoughts should count for no more than those of any other conservative economist.

The political genius of Mr. Clinton's plan is that it marries good policy with good politics. This used to be what Republicans called responsible budgeting. How sad that they now see it as unacceptable.