Ralph Nader really put his Washington power mystique, and possibly the future of the entire consumer movement, on the line this summer when he called the establishment of a federal agency for consumer protection the single most important consumer issue of the decade. He even threatened to personally capaign against Congressmen who he fears may cave in to big business lobbying pressure and vote against the wishes of their consuming constituents.

Nader and his 95-member consumer-labor-farmer-business coalition hope to win their 8 1/2-year battle to squeeze legislation creating an agency for consumer protection (ACP) through Congress this fall and see it signed into law by a willing President Carter. Since the bill has the backing of the administration and the Democratic party leadership in the House of Representatives, it was expected to pass easily this year. Instead, a massive lobbying effort led by the U.S. Chamber of Commerce has maintained enough potential "nay" votes to prevent Thomas P. O'Neill (D-Mass.), the speaker of the House, from bringing the bill to a vote.

Esther Peterson, Carter's effervescent consumer affairs adviser, said yesterday the bill's supporters may still be as many as 20 votes short in the House, according to an estimate made by longtime consumer advocate Rep. Benjamin Rosenthal (D.N.Y.).

The proposal would create a non-regulatory agency to advocate the interests of consumers before other governmental agencies, intervene in rule-making proceedings involving consumer affairs, and even take other federal agencies to court on the consumers' behalf.

The agency would also serve as a clearinghouse for significant consumer complaints and would obtain information from large businesses and federal agencies to help determine what the consumer interest is in specific issues, and when it is necessary and proper to intervene.

Big-business interests favor the kind of decisions consumer advocates claim the ACP would have fought had it been in existence, such as:

#The 1976 Federal Energy Administration's (FEA) removal of price and allocation controls from home heating oil. The FEA assured the public at the time that the price of the oil would increase by only two to three cents per gallon. After decontrol, however, the price of heating oil jumped by five to eight cents per gallon, making the added cost of this decision to American consumers more than $800 million, according to The Library of Congrvss.

#The decision of the Civil Aeronautics Board in 1974 to reject an application by Laker Airways to fly regularly-scheduled flights from New York to London for $125 each way. The board enforces regulations that prohibit most new air routes and proposed price cuts.

#The claim of Public Citizen, Nader's organization, that Interstate Commerce Commission regulations requiring trucks to return empty from delivery make mandatory and often out-of-the-way stops and which allow companies to cooperate in rate-setting, cost consumers several billion dollars yearly.

A consumer protection agency could intervene in the process by which such decisions are made, or even appeal them in the courts.

With such potentially high stakes, big business has responded with an intense and well-organized lobbying effort against the proposed consumer agency that has prompted many Congressional offices to report floods of letters, phone calls and personal visits from influential persons, including home district industrialists opposing the legislation.

As President Carter said with some dismay, "The lobbyists have come out of the woodwork."

"They have waged the most intense lobbying I have ever seen against any bill," Rosenthal said this summer. Without an effective lobbying strategy of their own, consumerists might have been unable to prevent the protection agency bill from suffering the same fate as the common situs picketing legislation backed by organized labor and killed by Congress last spring.

To prevent a similar upset, Nader approved what was for him an entirely new brand of lobbying--an old-fashioned grass-roots campaign with a new twist. Nader has spent a decade as a photogenic political entrepreneur, using the media to his best advantage as he lambasted what he saw as the many wasteful and dangerous practices of some of the world's largest and most powerful corporations. But propped up by institutions and the national media, and supported by a vague national majority. Nader has done most of his very effective lobbying along the corridors of Columbia and has felt little need to reach out to the home districts and put special pressures on specific Congressmen. But he is doing it now.

The new twist is what Nader refers to as "metallic irony." The consumer coalition last June 30 launched a genuine grass-roots campaign which targeted some 83 Congressional district. The goal was to get thousands of consumers "to shower Congress with nickels and letters" in support of legislation to create an agency for consumer protection. The drive is the brainchild of Congress Watch, a collection of eight lawyers who operate as Public Citizen's lobbying arm on Capital Hill, and of its director, Mark Green.