THE HOUSE Democrats are developing a shrewd and interesting response to President Reagan's economic strategy. Chairman James Jones of the Budget Committee, with the support of the Democratic leadership, has now brought out his counter-budget. Acknowledging the public demands for greater discipline in spending, they have gone as far as the president in cutting present spending -- although they have distributed the cuts differently. It's the sweeping reductions in taxes that are the vulnerable part of the Reagan plan, and there the Democrats are challenging him directly. This debate will refine the country's ideas not only about budgets but also about the deeper things that budgets only reflect, the ties of mutual obligation that hold this vast, disparate country together.

The Democrats have now made a central issue of the size of Mr. Reagan's budget deficit. It's a line of attack calculated to shake some of the administration's conservative support, especially in the Senate where there was already a good deal of uneasiness on that point. The deficit is hardly the only budget number that counts -- but neither is it totally irrelevant, as some of the supply-siders are currently arguing.

The federal deficit was rolling along at nearly $60 billion when Mr. Reagan took office. For all of the talk of fiscal rigor, the Reagan plan would not push it below $45 billion until the end of 1982, almost halfway through this presidential term. Even that number assumes all of the administration's most optimistic figures, with no nasty surprises like oil crises along the way. By most other people's calculations, the deficit would actually be rising, rather than falling, next year. The Democrats, proposing a smaller tax reduction, would hold that deficit to half the size that Mr. Reagan has projected. They are forcing the Republicans into the embarrassing position of defending another year of heavy deficit spending.

It's not only a budget that's being hammered together here. It's a program for the Democratic Party as well. The program, in this first draft, calls for stronger social intervention -- in nutrition, job training, legal aid and all the rest -- than the administration will accept. The Democrats would accelerate defense spending rapidly, but not quite so rapidly as Mr. Reagan intends to do. Above all, the Democrats -- following a trend that has been visible for a couple of years -- are now claiming to be the party of fiscal caution and conservatism, putting a balanced budget before a huge three-year series of tax reductions. They are trying to depict the Republicans as the party that's willing to take great risks with big deficits and untested tax theories. The tax bill is now the pivot on which the whole fiscal issue will turn, and perhaps the next congressional elections as well.