enator John McCain's decision to halve his campaign finance reform bill is a large risk with little hope of success.

If McCain's long-shot gamble produces a new law banning the hideous soft-money flood of toxic contributions, he will deserve the nation's applause. But the shift in strategy - forsaking the part of the McCain-Feingold bill that would regulate independent expenditures - did not immediately deliver any of the six to eight votes needed to get a bill through the Senate early next month. In fact, a few Republican and Democratic supporters of last year's McCain-Feingold bill, including Olympia Snowe of Maine and members of the Democratic leadership, have expressed disgruntlement at the move.

Oddly, McCain made his decision known the very day the House passed the full Shays-Meehan companion bill by a 75-vote margin. Whatever momentum might have carried over to the Senate side of the Capitol was instantly lost.

In addition, as Representative Martin Meehan of Lowell has pointed out, the two central provisions of the legislation are linked. If soft money is denied to the parties, some of it - perhaps most of it - will go to ''independent'' groups that will buy TV ads to influence the presidential campaign and many of the races for Congress.

Still, the corrosive effect of soft money is undeniable. The Federal Election Commission created the loophole when it bought the argument that the political parties needed to be able to raise money for ''party building'' efforts entirely separate from specific campaigns. The FEC has not had the courage to close the loophole despite overwhelming evidence in hundreds of races that the money is used to help candidates or hurt their opponents and despite the most obvious evidence that the ''party building'' argument is a sham: Since hundreds of millions of dollars began to flow through the soft-money spigot, voter participation has gone down.

If there is a chance of banning soft money, Congress should take it. Alone, it is a tepid reform; without it, no greater reform is possible.