The national consumer movement, faced with an administration hostile to its interests, has taken its most docile posture ever, Ralph Nader told the country's largest consumer organization at its annual meeting in Washington last week.

Appearing at the Consumer Federation of America's convention for the first time in six years, Nader, the dean of consumer advocates, blasted the organization's member groups for their lack of vigor in behalf of the spending public -- and at least some of the 250 people there agreed.

"We have to ask ourselves," Nader challenged, "how the worst consumer government of modern times could not produce the strongest consumer movement of modern times."

Nader's presence signaled a revitalizing effort and reunification within the movement after several years of internal friction stemming partly from disagreement over how to proceed in a political environment that has grown increasingly conservative since the movement's emergence 20 years ago.

The squabbling was evident as recently as last year, when a Nader-backed group picketed the federation because of its decision to present an award to Rep. John D. Dingell (D-Mich.), whom Nader has called the leading opponent of air bags in automobiles.

Some consumer leaders contend that they must take a more moderate position in order to be effective, while others favor the aggressive stance of the 1960s and '70s.

"In the beginning, the consumer movement could do no wrong; even our errors were forgiven," one consumer official said. "But the honeymoon ended with the Reagan election. We can't just stand there anymore and ventilate. To get results, we have to compromise, and we have to work more with business."

Nader, historically and relentlessly, has hewn to the more aggressive line.

In an effort to heal the wounds of the past the federation invited Nader to address this year's assembly with the understanding that he could speak his mind. Nader used the occasion to deliver his fire and brimstone sermon, urging that the "new wave consumer movement pay more attention to the old wave consumer movement."

The invitation to Nader was one of several signs of a new maturity within the consumer movement.

Officials of the Consumer Federation of America took care also to invite speakers of a more conservative bent, such as Terrence M. Scanlon, chairman of the Consumer Product Safety Commission. Scanlon, who favors voluntary industry compliance rather than government fiat, opened his remarks on federal regulation by saying that "my message may not be one this audience wants."

The two-day program represented a concerted effort by the federation to target important consumer issues and have experts discuss them. Workshops were organized to cover telephone issues at the local, state and federal level, as well as food hazards, consumer banking, energy taxes, indoor air pollution and power plants.

One participant, George Idelson, who produces a consumer newsletter, characterized this year's sessions as "more focused and less flailing" than the ones he has attended previously. Idelson said that consumer representatives are examining the pros and cons of issues more realistically and are working on building coalitions with allies in other areas, even in business.

But while many, like Idelson, may believe that coalition-building and compromise are necessary for consumer groups today, Nader expressed reservations.

"We have to be careful about fraternizing with the corporations . . . , " he warned. "It works when the two parties have equal power, not when they are unequal."

Nader said that consumer groups are not likely to have a successful relationship with firms such as General Motors.

"Where's the opportunity for consensus-building success with Generous Motors?" he quipped.

Other Naderisms:

* "I don't want to use 'consumer' anymore. I want to use 'buyer.' You don't go downtown to consume, you go downtown to buy."

* "The federal cop is no longer on the corporate beat. Instead, they talk about cooperating with business. They say 'no more confrontation.' Can you imagine the police chief of New York calling in a group of criminals and saying, 'No more confrontation'?"

* "Deregulation is a code word meaning no more law and order for corporations."

Nader praised some consumer leaders, among them Robert Hunter, the actuary who founded the National Insurance Consumer Organization. Nader also praised the state consumer utility boards, and Rep. Henry Waxman (D-Calif.).

But Nader also gave four examples of groups whose promise, he said, has "never materialized into a cutting edge for consumers."

The American Automobile Association, he declared, has failed to use the power of its 23 million dues-paying members to "force Detroit" to turn out safer, better automobiles. He rapped the American Association of Retired Persons, with its 18 million dues-paying members, for falling short of its potential to improve the status of all consumers.

Credit unions, Nader said, have a long history of providing consumer services, but have turned their back on that tradition and now spend their time "wondering how they can be more like banks."

And Nader said that the Bankcard Holders of America, an educational group with 100,000 members, "said they were going to protect consumers -- well, we've been looking for them."

Representatives of the four groups disagreed with Nader's assessments, contending they are using their potential on behalf of their constituencies. Lloyd Wright, speaking for the retired persons' organization, said his group has helped to overturn state laws that kept consumers from easily obtaining less expensive generic drugs.

AAA spokesman Allan Wilbur said officials of his association meet regularly with car manufacturers to press for improved car designs. Wilbur added that the AAA also has helped persuade some manufacturers to retain car bumpers that can withstand collisions at speeds of 5 miles an hour.

And Sarah Turner, a member of the District of Columbia League of credit unions, said "credit unions are doing things that consumers need."

Many of the consumer movement's leaders present for the speech gave Nader high marks.

"Ralph was issuing a call to action," said former Federal Trade Commission member Michael Pertschuk. "He was saying that the overwhelming hostility of the Reagan administration has put everyone to sleep, instead of driving us into action. He was telling us to get moving."

And Esther Peterson, who advocates consumer causes in the United Nations, described the Nader directive this way: "He told us to get off our duffs and get busy."