The message to the postman was unusual. Addressed simply to "THE Mr. Ralph Nader," the letter from a Washington state correspondent carried the instruction: "Postmaster: Please deliver this to him wherever he receives his mail in the East."

The letter was mailed in 1971, a year when Nader was riding high as the nation's chief consumer advocate. Lawmakers and citizens across the country eagerly sought him out for advice about a gamut of health, safety and economic issues.

Thus, it was not surprising that the vaguely addressed letter about meat-packing practices quickly found its way to Nader's Washington headquarters.

Today, as Nader prepares to celebrate the 10th anniversary of the creation of his empire, the mailman can still find the self-proclaimed consumer advocate, but his influence appears to be on the wane. His organization has lost battles more frequently -- even given up some ground -- and its financial support has declined.

One sign of the difficulties is Nader's scheduling for later this month of an elaborate birthday party for Public Citizen, his lobbying, research and litigating arm.

Concerned that the consumer movement he once drove now appears stalled, Nader is counting on the two-day birthday conference and subsequent $1,000-a-plate dinner to help rekindle the spirit and zest that once fueled it.

As one Nader official explained, the conference has been designed "to help get people organized to fight the Reagan administration."

Entitled "Taking Charge," the conference will feature workshops on the ways citizens can unite to gain greater control over government institutions, public resources and privately run but publicly held funds. Seminars will be given on how to organize food co-ops, gain access to broadcasting networks and organize at local levels.

"I'm really not very past-oriented," Nader said recently in explaining why the conference is focusing on the future and not on Public Citizen's record of successes.

Even so, the conference will have much to celebrate.

When Public Citizen was founded, it was a revolutionary idea. A group of attorneys just out of law school would lobby on behalf of consumers against powerful corporate interests that previously had encountered little public opposition. Rarely had such an organized exercise of consumer power been attempted.

A decade later, Public Citizen is a Washington institution -- one that has become synonymous with liberal, consumer and environmental causes. Meanwhile, it has spawned additional organizations representing myriad interests.

Today Public Citizen comprises six corporate entities: a lobbying arm, Congress Watch; a litigating segment, Litigation Group; a health and safety unit, the Health Research Group; a tax policy unit, Tax Reform Research Group; an energy group, Critical Mass Energy Project, which criticizes big-oil companies and nuclear projects; and a travel agency, Visitors' Center, which arranges tours for out-of-town visitors who want to see how their government works.

Public Citizen has given start-up money to numerous other groups, such as the Aviation Consumer Action Project and the Clean Water Action Project.

During its 10 years, Public Citizen has taught hundreds of young lawyers about the way Washington works, thereby creating a new generation of leaders and newsmakers, including Dr. Sidney M. Wolfe, who now heads Public Citizen; Joan Claybrook, who was administrator of the National Highway Traffic Safety Administration in the Carter years, and Mark Green, who ran for Congress last year and now heads The Democracy Project, which issues critiques of government and corporate policies.

Ten years ago "it was a fantastic experience, a heady trip" to work for Nader, one of his chief "Raiders," Harrison Wellford, recalled recently.

"Ralph had a unique hold on the country at that time," said Wellford, who served as executive director for Nader's first research organization, the Center for the Study of Responsive Law.

Founded in 1969 with foundation money, that organization still exists, conducting research studies for Nader. Public Citizen was created two years later -- with $1 million raised from two mass mailings -- to give Nader his own lobbying arm.

At the time, Wellford said, "there really was power." He recalled that two months after joining Nader and just out of law school, he had "full-dress" meetings with two Cabinet secretaries who had been Nader's adversaries but listened seriously to Wellford's proposals and ideas.

Hardly ever, Wellford commented, did he visit a government office without a reporter accompanying him. And in visiting members of Congress, Wellford observed that many had photographs of their meetings with Nader on their walls.

"When I was recruiting, I had the pick of the best and brightest lawyers in the country. One-third of the entire class of Harvard Law School was trying to sign up for summer jobs. For 100 summer positions, we had at least 5,000 applications," Wellford added.

They wanted to come even though it was well known that working for Nader was far from a plush job.

In 1971, salaries for newly graduated law students began at $4,500. Today the starting pay isn't much better -- $10,000 -- and top salaries are $25,000. Those who agreed to the low pay (and the same is true today) also accepted working conditions that tolerated little if any time off and included late-night phone calls from Nader, shabby offices and a very frugally run operation.

For instance, it took Nader years to agree to install a photocopy machine in Public Citizen's office. Accustomed to carbon copies, Nader was astounded when he got his first photocopy bill. He planned to pull out the machine and force his lawyers to go around the corner to get their material copied -- a move he hoped would force his troops to return to carbon paper.

But that ploy fizzled when Nader's top lawyer, Alan Morrison, told Nader, "The day the Xerox machine goes out, so do I."

Staff members were directed to save every scrap of paper so they could be reused, and pencils were never to be thrown out if they had any lead left in them. It got to the point that many staffers believed a colleague's facetious order that only pencils be used to write on legal pads -- so that when the pads were used up, they could be erased and reused.

Staff members who took some time off after working around the clock on special projects risked incurring Nader's wrath. One lawyer who had been Nader's point man in fighting the largest U.S. corporate merger up to that time -- International Telephone & Telegraph Corp.'s acquisition of Hartford Fire Insurance Co. -- made a weekend trip to the beach during the middle of the battle. The lawyer returned to find a cryptic note on his desk from Nader saying he assumed the lawyer went to the beach because ITT's chairman, Harold Geneen, was there.

But these hardships were offset by many victories, including opening up the government to more public scrutiny, getting the Food and Drug Administration to ban certain unsafe food additives and drugs, successfully lobbying Congress to eliminate tax loopholes, and playing a key role in shaping the nation's environmental laws.

The successes started to dwindle in the mid-70s, however, as the economy began to sour and many people decided the cost of many of Nader's projects was too high.

Hastening the decline was President Carter, who not only promised to be a better friend to consumers than Nader, but also appointed many of Nader's top officials to high posts in the government.

"The Carter years were kind of anesthetizing years for the whole citizen movement, because a lot of people went into the administration and the outsiders were just waiting and watching, once in a while prickling them but just waiting and watching," Nader complained in a recent interview.

The result was that Public Citizen, once the victor, frequently became the loser in its fight to give consumers a greater voice. Instead of being on the offensive, trying to get Congress to pass new legislation, Public Citizen was placed on the defensive, trying to keep what it had won.

The biggest loss for Nader came in 1978, when Congress killed one of his pet projects, a Consumer Protection Agency.

Some Nader allies privately attribute part of the troubles to Nader himself, saying he alienated many senators, representatives and supporters with his vitriolic attacks on those who opposed his policies.

Perhaps the most widely publicized attack was Nader's 1979 clash with Sen. Jake Garn (R-Utah), who three years earlier had lost his wife in an automobile accident.

Angered by a sharp comment by Garn in a Senate hearing, Nader lashed back by recalling that accident and saying, "I suspect, Sen. Garn, that some senator's personal tragedy might not have occurred if the auto industry had listened to us in the early years."

To this day, Nader does not regret that comment, which sparked an even more heated response from Garn. "The only regret I have is that it wasn't on television," Nader remarked recently, saying of Garn, "You're dealing basically with a beast of prey dressed up in a three-piece suit."

Nonetheless, that and other comments may have cost Nader some support. In 1971 Nader was able, through two mass mailings, to get 62,000 contributors and more than $1.1 million to get Public Citizen off the ground. Support continued to climb, and by 1974, Public Citizen had nearly $1.2 million from 175,000 contributors.

But in 1980, the latest year for which figures are available, direct-mail solicitations brought in only $710.

The low return is prodding Public Citizen into drastic action. For the first time, it hired an outside firm to do its mass-mailing this year. And in a highly unusual step for a group that has long boasted that it is funded primarily by $15 contributions, Public Citizen is throwing a $1,000-a-plate dinner at the end of its two-day conference to raise enough money so it and a sister group, the Center for Study of Responsive Law, can buy real estate here.

In an additional effort to raise money, Nader and Public Citizen's top officials are trying to get on television talk shows.

Getting on television is, in fact, one of Nader's prime goals. Access to television is "basic" for the future of the consumer movement, Nader says. Consumers need to have their own show -- 30 minutes a week -- to mobilize, he argues. "That is how people of like-minded goals discover each other. That's the way they will be able to band together -- that's the key," he contends.

To date Nader has had relatively little success in setting up organizations that will be an effective countervailing force to corporations.

Only one state, Wisconsin, has followed his idea and enacted a law to set up "Citizen Utility Boards," or CUBs. Offers to join such boards must be included in the gas utility bills. For $3 a year, consumers will be able to join the group, which is supposed to argue on their behalf before the public utility commission.

In existence for only a year, the CUB has already attracted 50,000 subscribers.

Nader last year stepped down as head of Public Citizen, turning over its reins to Wolfe.

Although Nader keeps tabs on the stands Public Citizen takes -- and often advises and gives testimony on the group's behalf -- he is staying out of its day-to-day operations.

Instead, he is spending his time trying to win new CUBs and public time on the networks. "The future role of the consumer movement is to build the instruments of political and economic power. It's not the time for the substantive issues right now, because there aren't enough resources to take on the problems. But if you have 40 to 50 CUBs around the country, you would never get a situation in which utilities would be getting major bailouts," Nader argues.

Although only one CUB has been set up after years of effort, Nader is optimistic.

"It's not wishful thinking," he says, to imagine newspaper headlines in 10 years talking about successful CUBs for different industries: "Insurance policyholders group negotiates reduced auto insurance premiums with major insurance companies. Tenants association group negotiates change in landlord lease terms. Supermarket consumers group persuades supermarket chain to stock more nutritious foods."

One reason for Nader's optimism is the new administration. "Reagan will help," he says. "I think they are going to make bad errors, and it's up to the citizen movement to take off from that."

Nonetheless, that prospect is not particularly pleasing to him. "It's like saying the KKK was being helped by the Civil War . . . . That's not the proper way to forecast progress, to say there must be suffering before there is a reverse of any movement. But that's the way it's going to be."