IN SOME RESPECTS, the oral arguments on the constitutionality of the McCain-Feingold campaign finance reform law that began yesterday before a special three-judge panel in Washington resembled spring training. How much of the law is upheld will be decided by the Supreme Court; yesterday's arguments were prologue. Still, both sides brought out their big legal guns for a case that could help define the shape of the American political system in coming decades. For if the political parties, interest groups and labor unions challenging the law prevail, they will effect a profound change in American society: Corruption will have been transformed into a legal right guaranteed by the Constitution itself.

Nobody can reasonably deny, after all, that contributors of unregulated, uncapped "soft money" expect access and influence in return. And nobody can deny, either, that so-called issue ads are a means of affecting elections while circumventing restrictions on corporate and labor donations to political campaigns. Money talks, and big money talks loudly and gets answers. Lawyers defending the law in court yesterday pointed to the 93 donors who each gave more than $100,000 to both parties. Their motivation can't be ideological; they are paying their ante so that Congress will let them play in the political game. Ordinary people who can't ante up don't get a seat at the same table.

Opponents of the law do not for the most part claim that this system of not-quite-extortion mixed with near-bribery is clean. Rather, they argue that such behavior somehow is speech protected by the First Amendment. For the courts to accept this and strike down the major provisions of the law, they would have to decide that nothing short of the most overt graft can be regulated and that politicians may take giant sums from the same people and companies whose interests they protect -- as long as they keep the linkage between the two implicit.

It cannot be that the Constitution forbids the political system to aspire to more -- that it demands a government beholden to special interests and unaccountable to the people whose sovereignty it proclaims. The plaintiffs in the case spent hours yesterday arguing from the periphery of the issues -- highlighting the rare genuine issue ad that would have to be paid for with regulated hard money under the new law, finding the truly state-level get-out-the-vote effort that could not be funded using soft money. And indeed, McCain-Feingold might well create some burden for groups that are not trying to corrupt the process. Yet that burden pales next to a judicial rule that would consign American politics broadly to its modern culture of influence-peddling. Congress, after years of debate and building a record, has said America can do better. The courts should not stand in the way.