The battle over campaign finance laws becomes a two-front war this week, with the Senate taking up a House-passed bill to ban big-dollar contributions to the political parties and the Supreme Court hearing a challenge to existing caps on how much people can give to candidates.

The legislative battle will range over familiar terrain and likely produce the same result--stalemate. The case the Supreme Court will hear Tuesday raises some fresh issues and forces the justices to revisit what many thought were settled matters.

In the controlling case on federal regulation of election finance, Buckley vs. Valeo, the high court held that Congress acted constitutionally when it legislated a $1,000 limit on individual contributions to a candidate, because the government has a justifiable interest in preventing corruption--or the appearance of corruption--in political campaigns.

The "soft money" battle in the Senate arises from the six-figure gifts some wealthy individuals, corporations and unions are giving--not to individual candidates but to the political parties. "Soft money" has clearly become a source of suspicion, and deserves to be banned--as the McCain-Feingold bill would do. The ban should be accompanied by an increase in the limit on individual contributions to candidates and parties and, ideally, federal matching funds, as the business leaders in the Committee for Economic Development have suggested.

But now the Supreme Court--for the first time in the 23 years since the Buckley decision--has to consider whether it was right to approve the $1,000 limit on individual contributions. Only two of the nine sitting justices were around when Buckley was decided, so it is possible--if not likely--that the answer will change.

The case stems from a Missouri statute putting a $1,075 limit on contributions to candidates for statewide office. On the face of it, as the Supreme Court said a $1,000 limit is reasonable for House, Senate and presidential contenders, a higher figure ought to pass constitutional muster.

But a 2 to 1 majority in the 8th U.S. Circuit Court of Appeals thought otherwise, and struck down the Missouri statute.

Two key issues are raised in the lower court decision: Is a limit of roughly $1,000 that was judged reasonable in 1976 still reasonable, when the costs of campaigning have risen enormously and inflation has knocked two-thirds off the value of the dollar? And is the mere suspicion of corruption, absent any evidence that politicians are being "bought" by big contributors, sufficient to justify limiting people's freedom to contribute to candidates?

On the first question, the evidence as I read it casts doubt on the lower court decision. During the three years the Missouri limits were in effect, candidates were able to raise more money for most races than in the past. A number of political scientists told the Supreme Court in an amicus brief they were convinced that the limits would not prevent "robust" campaigns.

The second question is more intriguing. The Missouri attorney general, Jay Nixon, contends in his brief that the courts should not second-guess others' judgment that contribution limits are needed to allay public suspicions about the integrity of the political process. Not only did the elected legislature deem such a measure to be necessary but the voters of Missouri in a referendum (later overturned by the courts) overwhelmingly approved even lower contribution limits.

But Sen. Mitch McConnell, the Kentucky Republican who leads the battle against the McCain-Feingold bill, raises an interesting point in the amicus brief he filed urging the Supreme Court to uphold the lower court decision. If the high court believed in 1976 that limits would help allay public suspicion of political corruption, 23 years later anyone would have to admit that public distrust of politics has never been greater. Why, he asks, continue the limits now that it is obvious they are not achieving their stated purpose?

When I asked Attorney General Nixon how he would respond to that argument--if one of the justices raises it Tuesday--he tried several answers: Public cynicism might be even worse if there were no limits. Legislation of this kind may not be a complete remedy, but "we're entitled to take incremental steps." And, he said, simply requiring full disclosure of campaign contributions is not enough: "One news story about a $100,000 contribution does not offset the impact of all the ads that $100,000 can buy."

I agree with the last two points, but doubt the first. And McConnell's question deserves a better answer. Maybe the Supreme Court will provide it.