JUST AS A HOUSE committee is debating this year's bill for partial public financing of House campaigns, a Federal Election Commission report has confirmed what everyone suspected about the activities of PACs-political action committees representing various interests and issue-oriented groups. Spending by PACs is rising quickly; their total contributions to Senate and House campaigns grew from around $22 million in 1976 to $35.1 million in 1977-78. Corporate and trade-association PACs gave about twice as much as labor groups. That is a new development. What is not new is that the bulk of all PAC funds went to incumbents. The average incumbent up for reelection got nearly 27 percent of his campaign funds from PACs; the average challenger raised less than 13 percent that way.

There is something here for almost everyone to worry about. Democrats, especially liberals, are concerned about the surge in business giving, which is more likely to advance Republicans and conservatives. Republicans fret about the interest-group support that helps sustain some Democratic incumbents. People who want to enliven political competition think challengers are getting shortchanged. And a growing number of Senate And House incumbents are also troubled by the growth of PACs and the general escalation of campaign costs. They dislike the whole business of soliciting funds from Washington interest groups, and feel harassed by the swarms of contending lobbyists on Capitol Hill.

With all these concerns on the loose, one might expect that the House Administration Committee could muster a quick majority for curbing the power of the PACs. One way would be to restrict each committee's total giving (now unlimited) and reduce its maximum donation to any candidate (now $5,000).

But few House members are likely to support that unless they are assured of public financing or some other way to finance campaigns. And that brings into play an even larger swarm of anxieties about ensuring challengers a firm financial base-but not too much to make incumbents nervous; trying to curb the influence of wealthy candidates-but also being able to compete with them; protecting all the parties and factions; and devising a new system that is enforceable-but doesn't cause a new regulatory overload. In short, those worried about the PACs are trying to ease the pressures of special interests without jeopardizing any of their own interests. It may not be impossible, but it's certainly going to be tough.