WHEN CONGRESSIONAL Republicans adopted, earlier in the year, a budget resolution calling for an unaffordable tax cut, doubting members were told not to worry. The resolution was not intended to be taken literally, the sponsors said. It was less a legislative than a political document, a set of goals that would help define the party and serve it as a compass in the lengthy budget negotiations ahead.

Now the overflowing tax bill itself has come up, and once again the doubters are being reassured. To keep some uneasy moderates in camp, an asterisk was added to the legislation before the House passed it by the barest of majorities yesterday. It says that part of the tax cut will take effect only if interest on the debt is declining. The effect could be to shrink the cut, since it's unlikely that a large tax cut and debt reduction could be simultaneously achieved. To some extent, the tax bill thus is also to be taken figuratively, the more so because the president has pledged to veto it if it reaches him in anything like its present form.

That's the plan. The Senate will take up its similar version of the bill next week. The leadership then hopes to reconcile the two and send the final version to the president before the August recess. His veto will set the stage for the serious negotiations expected in the fall.

There are people in both parties who expect those negotiations to produce a deal. We hope they're wrong. The deal would include a tax cut, not as large as the Republicans are voting but larger than the president has proposed, together with some version of the Medicare drug benefit that he wants to confer and an easing, tacit if not explicit, in the tight appropriations limits to which both parties continue to pretend to conform.

The problem is, there isn't room to do all this and maintain budget discipline. The tax cut would be financed out of a projected surplus of about $1 trillion in other than Social Security funds over the next 10 years. But most of the surplus will only materialize if (a) the president and Congress make deep domestic spending cuts, which they promised a couple of years ago but from which they already are backing away, and (b) if the savings from those cuts are used not to cut taxes but to pay down debt and thus reduce the interest payments that make up an eighth of the budget.

An array of programs, from Head Start and law enforcement to air traffic control and the upkeep of the national parks, would have to be cut by more than 20 percent in real terms. The promise was fake; it isn't going to happen -- and it shouldn't. If it doesn't, three-fourths of the imaginary surplus disappears.

The true cost of the tax cuts in the Republicans' bills would also be much greater than the surplus. The bills were carefully written in such a way as to mask their cost by delaying their full effect. Likewise, the Congressional Budget Office says that the president's proposed drug benefit would cost 40 percent more over 10 years than the White House has estimated.

A deal of the sort that at least some people have in mind would constitute a budget breakout. The politicians would buy themselves a signing ceremony with money that doesn't exist, and leave the bill to their successors. That's as true of the "compromises" already being floated -- a half-trillion-dollar tax cut over 10 years instead of the Republicans' $800 billion -- as of the bills the compromises would replace.

This is a year that began with pledges to solve the long-term fiscal problems the country faces -- mainly the problem of how to support the baby boomers in retirement. It threatens to end by making those problems worse. They should pass the appropriations bills and go home.