THE back and forth of the presidential campaign has yielded at least temporarily to a different kind of event. Today in New Hampshire, Democrat Bill Bradley and Republican John McCain plan to come together in a bipartisan appeal for campaign finance reform.

In one sense, this seems to push bipartisanship a little far. Once elected, politicians need to forge cross-party alliances if they are to achieve anything. But while they are campaigning, they are supposed to accentuate their differences and so give voters a choice. And yet this theoretical distinction between proper behavior in campaigns and proper etiquette in government breaks down in practice. In 1992 Bill Clinton perfected war-room campaign tactics; he then proceeded to govern by them. This is one reason why relations between the White House and Congress have sharply deteriorated.

Because campaign manners do influence the style and quality of governance, it is bad when candidates go negative; it harms their prospects in office just as surely as do reckless campaign promises never to raise taxes or cut benefits. Until recently, the Republican race has been somewhat more courteous than the Democratic one: Gov. Bush has gone out of his way to say that Mr. McCain, his chief rival, is a "good man," and Mr. McCain has declined to join his fellow Republicans in attacking Mr. Bush. This courtesy may, however, now be fading. The Democratic race was polite too at first but got less so as it tightened.

If electoral competition promotes negative campaign tactics, today's bipartisan event on campaign finance is a welcome surprise. In New Hampshire, independent voters can choose which primary to vote in, so Messrs. McCain and Bradley are competing head to head for votes. Their willingness to come together despite that should be commended, partly because it nudges the overall tone of the primaries in the direction of civility and partly because the cause espoused by the two candidates is deserving.

The two plan to pledge that, if each wins his party's nomination, he will call upon his party not to accept the unregulated "soft money" donations that were at the center of the 1996 campaign scandals. Even in the event that neither is nominated, this act of bipartisan campaigning is useful. It will be laced with references to another cross-party pledge, made by Mr. Clinton and Newt Gingrich in New Hampshire in 1995, to cleanse campaign finance. By reminding voters of this broken promise, Messrs. McCain and Bradley may stoke fresh indignation about the current campaign money system.