THE SUPREME Court yesterday stripped congressional opponents of their principal excuse for not acting on campaign finance reform. Their argument had been that regulation of campaign giving, even for the high public purpose of preventing corruption or the appearance of corruption, was a violation of the free speech clause, since in politics money is equivalent to speech. A 6 to 3 majority of the court, including Chief Justice William Rehnquist, chose to the contrary to reaffirm in strong terms the Watergate-era decision that such regulation is constitutional.

There will still be plenty of arguments about the point at which regulation goes too far and does infringe on speech. But plainly there is room to repair the law that both parties have shredded in recent election cycles. The House last year passed, over the objection of the Republican leadership, a bill that would begin to do so. The bipartisan majority that appears to be in favor should override the obdurate Senate Republican leadership as well. The need could not be greater; the law this year has become a nullity that neither party feels compelled even to pretend to observe.

The court yesterday upheld a Missouri law imposing limits on contributions very similar to those nominally imposed at the federal level. In the process, it reaffirmed in broad language its landmark holding in Buckley v. Valeo that preventing corruption and its appearance is a governmental interest sufficiently compelling to justify reasonable constraints on the role of money in politics.

The court did not say directly that further regulation--the effort to ban the use of so-called soft money, wherein the national party organizations are used to raise and spend on behalf of their candidates funds the candidates are forbidden to raise and spend themselves--would pass muster, though some of the justices, writing separately, did so. But the opinion by Justice David Souter states clearly that countering the perception that politicians are being bought is a proper justification for regulating donations. "Leave the perception of impropriety unanswered, and the cynical assumption that large donors call the tune could jeopardize the willingness of voters to take part in democratic government," Justice Souter writes. It is hard to see why this observation, if true for individual contributions to candidates, would be any less true for corporate or union contributions to political parties.

The obstacle to achieving a less corrupt campaign finance system is not the Constitution but the people using the Constitution as an excuse. Opponents had thought the court might use the Missouri case to back off Buckley v. Valeo. But only three justices--Scalia, Thomas and Kennedy--indicated a readiness to do so. The rest rightly said that a willing Congress can solve this problem. Will is the missing ingredient, not authority.