Washington — Decades have not dimmed the fierce light of Ralph Nader's zeal. It has been almost 20 years since he doomed the Corvair with his book ''Unsafe at Any Speed,'' yet he still carries a workload that makes chain-gang labor look luxurious. He still pounds his targets with words as blunt as ever.
He has even become a United States export. Recently he returned from a trip to Australia, where he says he got in a ''row'' with the prime minister over something to do with uranium.
But back home these are trying times for Mr. Nader and the public-interest movement he symbolizes. Many public-interest groups were demoralized in 1980 by -Ronald Reagan's smashing victory, and since then they have had to play almost constant defense against White House actions.
''The government is in the control of the corporate system, sure,'' Nader says, with the sort of matter-of-fact voice in which other people say things such as, ''The sky is blue.''
With such a clearly defined foe, citizen groups have been forged into tough, creative guerrilla units, he claims. ''We've succeeded in blocking them from rolling back the last 25 years of government regulation,'' Nader says. ''Sometimes a movement fights better when its back is against the wall.''
Though some have roots in the 19th century, most of the pressure organizations today grouped under the ''public interest'' label rose to prominence during the stormy years of the Vietnam war and Watergate. They tend to be associated with liberal causes, and they range from environmental groups to consumer organizations to the big, all-purpose lobbies of Common Cause (the largest group, with 250,000 members) and Public Citizen (Ralph Nader's umbrella organization).
In their passionate early years, these groups helped pass laws on everything from air quality to campaign financing reform to airline ''bumping'' of passengers. Their lawsuits gave Richard Nixon a swift shove toward his political exit. For instance, Ralph Nader's Public Citizen persuaded a federal court to rule that the firing of Archibald Cox was illegal.
But by the late '70s, the passion cooled and success came harder. Congress failed to pass legislation creating a national consumer agency, one of Ralph Nader's primary goals. President Carter, who appointed many public-interest activists to government office, proved less than an activist himself.
''Under Carter it was like, blah, there was no spark and not all that much was happening,'' Nader complains.
Then the cold water of the 1980 election hit the public-interest sector square in the face. Suddenly most of their actions were rear-guard - fighting budget cuts, deregulation proposals, personnel appointments.
At the same time, the movement's image was not what it once was; nearly half of those who responded to a 1982 Harris poll agreed that consumer leaders were ''out of touch with consumers.''
Nader admits that the Reagan administration has forced public-interest groups into a much more defensive posture ''than what could be.'' But he says many White House proposals have been fought to a standstill: Clean Air Act revisions remain stalled, the departments of Education and Energy haven't been dismantled, the Freedom of Information Act hasn't been damaged.
And in any case, he says, adversity is a great concentrator of the mind, and defensive victories can have a particular sweetness and public impact.
''The defensive victories by the environmental groups against (recently resigned Interior Secretary James) Watt and (former Environmental Protection Agency (EPA) chief Anne) Gorsuch have actually strengthened the environmental mind in our country,'' he says. ''It's taught Reagan something he probably didn't know - there's a political force there he can't ignore.''
Indeed, environmental groups' institutional fortunes have soared under Reagan. The Sierra Club's pre-James Watt membership was 181,000; now it's 365, 000.
How have other types of public-interest organizations fared? What do other activists think is the state of the public-interest movement?
It was not the sort of bake sale where Republicans would feel at ease. The wares had names such as ''guns-or-butter cake,'' ''flat-broke bread,'' and ''dense-pack brownies.'' Games included the help-Jim-Watt-put-his-foot-in-his-mouth shoe throw and the trickle-down coin toss.
The Let-Them-Eat-Cake Sale, held in Washington, was but one of 63 such foodfests held around the country on Oct. 3. The sales, national director Peter Harnik says, had a two-pronged purpose: to raise money for local public-interest and liberal groups, and to raise public consciousness about Reagan administration moves.
''These are dark days for public-interest groups,'' sighs Mr. Harnik. ''The government's not as receptive. The media are not as receptive.''
Harnik himself is a public-interest veteran, once a Nader foot soldier, then an staff member of Environmental Action public-interest group, and now a free-lance organizer. He says he's pleased with the bake sale results - about $ 100,000 was raised nationwide, with 40 local sales still to go.
But for the movement as a whole, ''it's harder to make progress'' today, he says. ''We've had to scale back our visions.''
Where once he would have plotted how to get autos banned from a city's downtown, for instance, Harnik says he would today focus on just getting a bike lane.
''And the scrutiny of corporate abuse has really faded from the public-interest agenda,'' he says. ''The battle against pollution should be focused on corporations, not the EPA.''
The powerful Corvette basks in the sun like a shark at rest, the US Capitol looming in the background. It is notable in three respects: It runs on methanol instead of gasoline; it belongs to actor Charlton Heston, an advocate of alternative fuels; and it is about to be donated to the Center for Renewable Resources, a branch of the Solar Lobby. ''I've changed my mind,'' jokes Mr. Heston in the middle of the press conference announcing the gift. ''I can't let her go.''
A tall, dark-suited man grabs the microphone. ''Don't worry,'' says Scott Sklar, political director of the Solar Lobby, ''you'll have visitation rights.''
That the lobby could entice Mr. Heston, a staunch conservative, into giving up his Corvette for the cause is evidence of the group's flush fortunes. President Reagan has slashed solar and renewable-energy programs to a shadow of their former selves, but Solar Lobby's membership and budget have doubled in the past three years.
''After President Reagan came in, the weaker citizen groups fell out of the system,'' Mr. Sklar says. ''At the stronger ones, membership increased. Reagan's policies activated their constituencies.''
But Sklar says he fears constant defensive play has made groups too pragmatic , hesitant to dream dreams.
''My work used to be 40 percent practical, 60 percent futurist-oriented. Now the split is 70-30,'' he estimates.
Part of this shift is undoubtedly caused by a natural aging process, as citizen groups become more institutionalized. Sklar says the people coming into the movement these days are much more conventional - he just hired a press secretary who used to work at Sun Oil.
''In the late '70s we started wearing a three-piece suit and playing the game ,'' he says.
Under 40, Mark Green is one of the next generation of citizen-group advocates. Schooled in Ralph Nader's campaigns, he rose to the post of director of Congress Watch, Nader's lobbying regiment, before resigning for his ill-fated try at elective politics.
''A lot of (citizen) groups are finding the going harder today, but part of that is just natural ebb and flow,'' says Mr. Green. ''Reagan has infused the movement with a lot of new energy.''
His own response to Reagan's election was to found an educational institute, The Democracy Project, dedicated to scrutinizing White House actions. This month , for instance, the group has published a study documenting industry's easy access to regulators.
''President Reagan now controls the national microphone,'' Green says. ''We have to answer his errors.''