IS HALF A LOAF worse than none? That's the question posed by the surprise Senate vote yesterday in favor of a measure that would cap President Bush's proposed $726 billion tax cut at $350 billion, and the answer, apparently, is no. While this country is fighting a war of unknown duration, while overall tax revenue is down thanks to recession, while hundreds of thousands of people risk losing their health insurance because of state fiscal crises and proposed Medicaid cuts, it is irresponsible of Congress even to consider passing a tax cut worth $350 billion -- let alone $726 billion -- over 10 years, thereby creating a vast budget deficit for the next decade and possibly beyond.

Having said that, it is also true that yesterday's 51 to 48 vote represented a stunning reversal of the Senate's position. As recently as Monday, the Bush administration was certain that the full tax cut package would pass -- so certain that officials finally deigned to admit that the war in Iraq could cost at least $75 billion, adding further heft to future budget deficits. That news, combined with some fiddling with amendment language, seems to have helped persuade Sens. Ernest F. Hollings (D-S.C.) and Lincoln D. Chafee (R-R.I.) to switch sides and back the cap, because to do otherwise would have ensured passage of the full tax cut.

But a budget resolution isn't a budget resolution until both houses of Congress resolve their differences. Until that happens -- possibly this week -- the Republican leadership will do its best to raise the tax cut, in part by calling for new votes on yesterday's amendments, in part by introducing new amendments, in part by trying to steamroll the Senate into voting for the full tax cut later. To keep the numbers down, Republican moderates will have to stay firm and continue to vote against any further increase in the tax cut figure, however cleverly the amendments are worded. Once again, a few moderate senators hold a tremendous amount of power in their hands. We hope that they will, at the very least, prevent congressional Republicans from chipping away at the cap, and vote today against amendments that could make the tax cut larger. But we would much prefer that they vote their consciences, do what's right for the country and take every opportunity to vote against this ill-conceived tax cut altogether.