Ralph Nader and a coalition of groups announced here yesterday a new campaign to pressure "wavering" members of Congress to vote for a consumer protection agency, which the consumer movement regards as the most important consumer issue of the last decade.

Nader said at a press conference that consumer activists in each of 78 congressional districts would send letters and nickels to their representatives, urging them to support the legislation, now stalled in Congress. Nader called the nickels a form of "metallic irony," because he said the agency, with a proposed budget of $15 million a year, would cost each American five cents in taxes.

"Big business is throwing millions at Congress," Nader said. "If the people throw nickels, they will prevail."

The proposed agency would have authority to speak on behalf of consumers before government boards and regulatory agencies and challenge adverse court decisions.

Consumer activists have been trying since 1970 to get approval for the consumer protection agency.

The current bill was expected to breeze through Congress this year after President Carter endorsed it. But intensive lobbying by business interests dimmed the prospects of passage of the bill. In May, it squeaked through the House Government Operations Committee by 22 to 21.

Earlier this month, Senate Majority Leader Robert C. Byrd (D-W.V.) told Carter that the Senate would not consider the bill until it passes the House.

Mark Green, director of Nader's Public Citizen Congress Watch, said that the 78 House members on the list are undecided on the bill, even though 45 per cent voted for a form of the bill at one time or another. Three-fourths are Democrats, and 55 per cent are in their first or second term.

Green said the "nickel campaign" would last until Aug. 1 or a successful vote, "whichever comes first." Nader promised that consumer activists would appear in the congressional districts at election time to let voters know how their representatives voted on the measure, which he called "the ultimate consumer litmus test."

Joining Nader at the press conference were representatives of other groups supporting the legislation, including the Consumer Federation of America, the AFL-CIO, the United Auto Workers, Common Cause and the American Association of Retired Workers.