Budget deficits are the great equalizers in Congress; they make the people in power miserable regardless of party, ideology or recent success at the polls.

In years past, it was the Democrats who suffered. Liberals pressed to increase spending; conservatives, to reduce the deficit. The congressional budget committees' preliminary spending and revenue targets were regularly attacked on both wings, especially in the House. The Republicans made political hay out of the Democrats' dilemma.

Now it is the Republicans' turn to squirm.

True enough, President Reagan and his allies in Congress want to cut spending. But they also want to cut taxes. And so they are bumping up against that same old demand for lower deficits, putting them in basically the same squeeze that so pained the Democrats in previous years.

The irony is not lost on the Democrats, many of whom now leap at every opportunity to champion the cause of balanced budgets -- just as the Republicans did when they were out of power.

The problem is that, except for true believers in the supply-side school of economic prosperity through tax cuts, most members of Congress appear to be as reluctant to build up the deficit by cutting taxes as they are to overload it with more spending.

"What you have is something like a 2-to-1 margin in every poll indicating that people prefer balanced budgets to tax cuts," largely because they believe that deficits help cause inflation, explains Reps. Les Aspin (D-Wis.), a member of the House Budget Committee.

It is in this context that Reagan's economic program, despite widespread support in Congress for most of his proposed spending cuts, took its first fall on Capitol Hill last week.

In the House Budget Committee, the Democratic majority came through with a preliminary budget for fiscal 1982 that, according to the Democrats' arithmetic, cuts Reagan's projected deficit by half. It does this largely by trimming down his proposed tax cut.

Although the first blush of enthusiasm has faded a bit, pro-Reagan sentiment is reported to be running so strong in the Democratic-controlled House that the Democrats' proposal is given only a fighting chance when the budget comes up for action on the floor after Congress returns from its Easter recess April 27.

But the reduced deficit is regarded as one of its strongest arguing points with the 40 or more conservative Democrats who may well decide the budget issue. And the Republicans' ability to maneuver is restricted so long as they stick with the full tax cut recommended by Reagan.

The situation in the Senate illustrates the Republicans' dilemma even more vividly -- in part because it pits Republicans against Republicans in what amounts to a truth-in-budgeting exercise involving projected deficits for 1983 and 1984 as well as 1982.

For one thing, the Senate Budget Committee, even though it is controlled by the GOP, couldn't swallow all of the Reagan administration's economic and spending-rate projections, especially its confidence that interest rates will fall dramatically as the economy begins to respond to the Reagan program. As a result the committee projects a deficit for fiscal 1982 of $60 billion rather than $45 billion, as the administration projects.

Worse yet are the projected deficits for 1983 and 1984. The administration has promised to reduce these through further spending cuts, but as yet has offered few details about where such cuts might be made. As a result, the committee's budget projection for 1984 showed a deficit of $44.7 billion, not the first surplus in 15 years, as Reagan has promised.

This was too much for Sens. William L. Armstrong (R-Colo.), Charles E. Grassley (R-Iowa) and Steven D. Symms (R-Idaho), who want the future budget cuts spelled out so that -- at least in theory -- a balanced budget can be guaranteed by 1984.

"We are not on a path that puts us in balance," complained Armstrong. "We have to get on a path that does."

Senate Budget Committee Chairman Pete V. Domenici (R-N.M.) took the position that a deficit is a deficit until proven otherwise, warning that future spending cuts are hypothetical until nailed down in a budget resolution. So he and most other Republicans refused to budge.

At this point, the committee's Democrats, badly split only two weeks earlier when the committee was dealing solely with spending cuts in its so-called "reconciliation" instructions to legislative committees, suddenly found unity. Objecting both to the administration's tax cut and to its economic projections, which they considered too rosy, they voted to a man against the budget proposal.

With the three Republicans joining the Democrats, the budget was defeated, 12 to 8, last Thursday night.

Now the committee will have to come back after the recess and try again. Choices include scaling back the tax cut (which neither Armstrong nor the administration wants) or finding more spending cuts (which could cause trouble among both Republicans and Democrats whose constituencies would feel the pain).

One problem with finding more spending cuts is that the easy ones have already been used up. Domenici said, for instance, that he voted last week to scale back cost-of-living increases for Social Security and other politically sensitive benefit programs in part to dramatize where the committee would have to turn if it opted for more cuts.

"There's no question that there's a problem," said Sen. Ted Stevens (R-Alaska), the assistant majority leader, after the committee vote last week. "The problem is the conflict between reduced taxes and getting the economy going on the one hand, and the commitment to a balanced budget" on the other hand.

Under the supply-side theory, deficits would take care of themselves as tax cuts generate a healthier economy and, as a result, more tax revenues. Republicans no longer "worship . . . at the shrine of balanced budgets," said Rep. Jack Kemp (R-N.Y.), one of the theory's leading proponents. But the balanced-budget religion dies hard. "It takes confidence in the [supply-side] theory that some don't have," said Stevens.