How many PACs would Common Cause back if Common Cause could back PACs? None. The citizens' lobby Common Cause has launched a major, media-oriented advertising drive to build grass-roots support for tighter curbs on campaign contributions from political action committees to congressional candidates.
The initial thrust, to which $600,000 is committed, is to make funding activities by corporate and labor-union PACs an issue in the upcoming Democratic presidential primaries and caucuses.
''Our message is simple: No matter who is elected president this year, (he) will face a Congress that will be deeply indebted to special-interest political action committees until the campaign financing system is changed,'' explains Fred Wertheimer, national Common Cause president.
Of the 3,371 PACs registered with the Federal Election Commission at the end of the 1982 congressional campaign, nearly one-third donated to incumbents, Wertheimer says. 64 of those gave in excess of $100,000, he points out, citing a recently released study by his organization.
Through the presidential primaries and caucuses, Common Cause aims to spotlight what it views as a serious problem and to help elect more Congress members who are committed to restricting PAC contributions.
The strategy is to concentrate on only a few states at a time throughout the coming months - starting with New Hampshire and Iowa, the first in the delegate-selection process - using television, radio, and newspaper advertisements.
Common Cause leaders had hoped to capitalize on the Jan. l5 televised debate among the Democratic presidential candidates to get a head start on turning campaign financing into a high-visibility issue, Mr. Wertheimer says. ''We had l5 people in the audience ready to raise the question, but none were called on, '' he laments.
The Common Cause media campaign in New Hampshire and Massachusetts began Jan. 18 with a five-minute paid television presentation featuring four former members of the US House and one incumbent. They decry the increasing role of political action committees in financing congressional candidates.
Although most of the participants in the presentation are Democrats, as are many of backers of Common Cause efforts, Wertheimer emphasizes ''this is a nonpartisan issue.'' He notes that US Rep. Charles Leach of Iowa, who appears in the TV spot, is a Republican.
The GOP congressman, who accepts no PAC contributions for his campaign, suggests that financing from such sources may tend to exert improper influence over legislation and policy decisions.
Representative Leach is a sponsor of the Common Cause-backed congressional campaign financing legislation that would restrict the total amount a PAC could give to a candidate for the US House. The pending measure also would limit the amount a congressional candidate could spend on an election campaign to $240,000 . It would also encourage such funds to come mostly from small contributors. An individual federal income-tax credit up to $100 would be provided.
A Common Cause study released last November showed that political action committees favored incumbent congressmen by 3.4 to 1, while other contributors, including individuals and political parties, favored incumbent by only 1.3 to 1.
Since prospects for passage of the legislation this year appear remote, Common Cause leaders say they are all the more eager to help House members who support limitations on PACs get elected next fall so there can be a major push in 1985.