DO YOU STILL WANT Congress to keep cutting your federal budget, deeply and rapidly? President Reagan believes that you do, and appeals for your support in goading your increasingly uneasy senators and congressman. But the president's skillful address on Thursday evening was conspicuously vague about the specific reductions that he now proposes.

The largest part of the next round of savings, as Mr. Reagan presents them, would be a cut across the board in all programs that are not protected either by law or, like defense, by presidential policy. The remaining vulnerable programs amount to about one-tenth of the budget, bearing out the warnings that any mechanical budget-cutting formula inevitably means deeper and deeper cuts in smaller and smaller areas. Since Congress balked even last spring at some of the reductions indicated here, it hardly seems realistic to expect a broad sweep now.

Mr. Reagan, in his address to the country, didn't quite address the impression that this year's tax cuts favor the rich while the spending cuts will lie most heavily on the poor. He repeated his conviction that the cuts will affect only the malingerers and cheaters, not those unfortunate people in real need. But current evidence is running the other way. Another item in his new list of cuts is a further shaving of the entitlements--food stamps, welfare and the rest. Congress now needs to consider how much farther it wants this process to go.

Why are the president and Congress confronted, so late in the season, with the prospect of a sharply rising deficit and an urgent need to find additional savings? Because the president and Congress went too far in cutting taxes. A lot of people in Congress now seem startled to see the scale of the savings still required. It is fair to ask them what in the world they thought they were voting for, when they whooped the tax bill through in July. The answer is that most of them were only voting with the president. Now it appears that the president has no very precise ideas about what's to be done next, beyond saying that it is essential to keep squeezing. As a result, his congressional support suddenly begins to look much less solid.

But there's one thing on which Mr. Reagan is absolutely right, and that's the need to begin bringing down the budget deficit next year. Otherwise, interest rates will stay intolerably high.

Fortunately, there's a better way to do it than to keep going after the social benefits and the entitlements. Mr. Reagan's latest plan proposes raising several billion dollars by tightening the tax code, and another billion through user fees for planes and boats. Why stop there?

Why not go for the full $2 billion in user fees that he proposed in March? Why not pick up several billion more by limiting the misguided tax deduction for consumer credit? Why not still another several billion by withholding taxes on interest and dividends, to curb tax evasion by investors? Mr. Reagan has done much for investors. It is not unfair to tighten up the notoriously slack collection of their greatly reduced income taxes.

That's the way for Congress to begin thinking about the choices ahead. It's dividend withholding versus another round of cuts in school lunches. It's the subsidies for corporate jets versus another round of cuts in Medicaid. It's the tax deduction for consumer credit versus another round of cuts for food stamps. Are those really impossible choices?