If members of Congress didn't like the flood of five-cent pieces Ralph Nader brought down on them two years ago (and they didn't), they will simply abhor what he's doing now.

Nader's Public Citizen Congress Watch lobbying organization today will open a campaign to generate a mail avalanche of dollar bills in support of public financing of congressional elections.

For starters, Nader will be in Philadelphia today and Chicago Monday to urge Congress Watch suporters to pepper 10 House members from those two cities with dollar bills.

Mark Green, director of Congress Watch, said those 10, plus at least 20 more who will be named later from other areas, are "swing" legislators who can make a difference on the campaign-financing bill.

The Chicagoans are Reps. Dan Rostenkowski, Marty Russo, Frank Annunzio, Bennett M. Stewart and Morgan F. Murphy, all Democrats.

The Philadelphians are Lawrence Coughlin and Charles F. Dougherty, Republicans; and William H. Gray III, Raymond F. Lederer and Michael O. Myers, Democrats.

"Some of them are for, some are against the pending public-financing bill HR 1, but most of them are moderates who can go either way on issues that are important to us - swing members," Green said.

The idea behind the Congress Watch campaign is to persuade those and other legislators that there is strong grass-roots support for campaign-financing legislation, he said.

Congress Watch adherents are being asked to send in real dollar bills or facsimiles to which small strands of string have been attached.

"The dollars with strings are intended to symbolize the idea that real campaign contributions have invisible strings attached. Members of Congress get insulted when you suggest there is a connection, yet they complain to us privately about the role of money in politics," Green said.

Two years ago, when Congress Watch was pushing for approval of a Consumer Protection Agency bill, an estimated 40,000 nickels were sent in by supporters to show where they stood. The measure lost, however, by 37 votes.

The nickels caused problems in many offices - jamming the mails, embarrassing members who didn't want attention, requiring replies and raising questions about how to dispose of the money.

Aside from the inflationary jump from nickels to dollar bills, the difference this time is that the campaign marks Nader's first attempt to organize local chapters of Congress Watch.

In Philadelphia, for example, nine consumer groups are joining to form a Congress Watch local. Green said that three dozen chapters, mostly in large cities, will be organized by the end of 1979.

Those local groups will not be political organizations, Green said, but will work to generate support for Public Citizen positions on consumer issues. A House floor vote on the public-financing bill is expected by early summer.