Waitress in hotel bar: "May I ask you - were you in here before?" "No." Waitress, triumphant: "Then I know where I saw you." His answer is quick: "On the 'Phil Donahue' show." Waitress: "Nooo." His answer is even more positive: "The 'Today' show." Waitress: "No." but the lightbulb is forming. "i know - 'The Advocates'! " He: 'The advocates.' Exactly."

Waitress: "Were you anti-nuclear?" He: "I certainly was." waitress, with accompanying squeal: "On, I loved you. You just showed those other guys. I'm against it - as much as I know about it. Yeah. You sure did a good job."

She is back a few minutes later for an autograph. This time, no lightbulb forms. The name - Barry Commoner - means nothing to her.

Commoner - the leading advocate of solar as the way to lead us out of the energy tunnel - will tell you that this is pleasing to him; that the message is more important than the man. He can afford such protestions because most of his fans do know him by name.

Once called the Paul Reverge of ecology, Commoner is the scientist-activist supreme, the professor who talks to millions. Hero of the environmentalists, darling of the New Yorker set, scourge of chemical and petro-power people, his public popularity crests with each new crisis.

Commoner has been in the forefront of many causes for a quarter of a century. In the '50s it was ban the bomb and radioactive fallout and strontium 90. In the '60s and '70s it was the peace movement and pollution and population explosion. Commoner warned you about mercury in tuna and that fried ham-burgers could do more than settle into grease balls in your stomach; they could be carcinogenic.

He rode through the streets at a time when many did not want to listen to an ecological Revere sounding the alarm on sewage and fertilizers and chemical pesticides and auto pollution and auto power plants.

Now Commoner is in a shoot-out with Big Oil, Energy and Carter - while being touted as a possible presidential candidate of an incipient political party. Recently, Commoner dashed through Washington, giving a number of speeches, making media appearances, trailed by the devoted.

Commoner's solar talk doesn't just mean discs placed on flat roofs to catch the sun. "There is an excellent octane booster," he tells a National Press Club luncheon. "Some of you drank it just a little while ago. Alcohol. Booze." He is then into a basic pitch: "By 1990, 40 percent of gas could be alcohol - which is solar. It comes from corn. Unless we start giving farmers the capability to produce alcohol on the farm, we are going to be in a series of gasoline crises the likes of which we have never seen."

In 1970, Commoner made the cover of Time magazine. This time - as he glibs his way through talk shows - Commoner has entered the pop culture. People gawk in recognition as he steps out of limos - a 60-year-old of stocky build and imposing manner in tan corduroy suit, thick head of white hair, dark eyebrows, horn rims. He leaves the Washington Hilton bar and his vodka-on-the-rocks to make phone calls ("to London," he offers, and to his office.)

Commoner is a man of ideas who has learned how to sell them to the public in palatable prose; a scientist who has perfected the art of book flackery as surely as any pot-boiler novelist. On return from the telephone, the smile plays. "The publisher is inundated with response to the Donahue show."

One of Commoner's earlier praised works was "The Closing Circle," which took up the Rachel Carson ecological crusade. In his just-published book, "The Politics of Energy" - his third book excerpted by The New Yorker - Commoner charges that Secretary of Energy James Schlesinger "fudged" data to make Carter's energy plan sound more environmentalist-oriented and better than it was. Commoner - in provocative lectures where alcohol becomes "booze" and technical facts are laced with everyday analogies - says solar is the only answer.

Commoner predicts nothing new from Carter when the president comes down off the mountain and addresses the American public. Carter's expected emphasis on syn-fuels is typical of a "failure" of approach to the energy crunch - an approach that "illuminates Carter's incompetence," says Commoner. "A 'new' Schlesinger can also expect to fail."

Commoner's pet gasohol solution has been ignored by the administration, he says, because it would "break the monopoly of the oil companies." Such ideas are "kept away from the American people because the Carter administration is so incompetent that it wants the rest of us to share in that abysmal state!"

Commoner will come out swinging on the new Tom Snyder news show immediately following Carter's scheduled Sunday speech.

Commoner grew up tough and poor in New York during the Depression. His mother was a seamstress, his father a tailor - until he went blind. Commoner roamed with a street gang, but he also showed an early intellectual curiosity. "I had a little microscope and I used to look at stuff out of the goop in the Brooklyn Botanical Garden."

Commoner's thirst for knowledge was heightened by his uncle, Avrom Yarmolinsky, "a great Russian scholar, head of the Slavonic division of the New York public library. My uncle and aunt - he was married to Babette Deutsch, the poet - urged me to try for Columbia instead of City College. But Columbia also had this ghetto school in Brooklyn - they sent Brooklyn Jews there. The only way I got into Columbia was through my aunt who lectured there; she stamped her foot and got me admitted."

Commoner put himself through Columbia with odd jobs, graduating in 1937 with honors in zoology. "Every semester I'd get a letter congratulating me on my brilliant record - and the next week I'd get a letter rejecting me for a scholarship. People have forgotten the anti-Semitism of that time."

His Russian-born parents, unlike many Jews who fled to America, were not political activists. Columbia helped form his socialist leanings. "I was there at a pretty radical time - the Harlan County strikes, the Scottsboro boys, the Spanish Loyalists. That sort of radicalized me."

Harvard came next. Commoner closeted himself in a laboratory for three years and emerged with a Ph.D. in cellular physiology. He later married a pschologist and amateur cellist.

After World War II and the Navy, Commoner began teaching at Washington University in St. Louis. Awards for cellular research followed. He now belongs to that international set of scientists who convene at world-wide conferences. In the mid-'50s, Commoner achieved public attention when he conducted a nationwide survey proving that strontium 90 had lodged in U.S. babies' teeth. The nuclear test-ban treaty is one effort Commoner regards as a major victory.

Commoner founded Washington University's Center for the Biology of Natural Systems at St. Louis in 1966, the first of its kind in the United States. At Commoner's center, scientists work on scientific issues with a Nader-like sense of public concern. But laboratory anonymity is no longer for Commoner; about half his salary comes from royalties and lectures. He hopes to arouse the public with his message. "There are answers to the stupidity with which this administration is ruining the country."

Asked if he is a socialist, Commoner chuckles and says he's a "half socialist." He doesn't believe we have to nationalise the oil companies. "The answer is to make them into public utilities - to produce oil and gas and make a fixed rate of profit like any utility and that's that."

Fuel for Commoner's solar solution comes in daily headlines: Gasoline refiners, wholesalers and retailers stand to make $8 billion to $15 billion in extra profits a year from the gas shortage, says an unpublished DOE analysis.

And so the public is primed. Fans praise and critics bemoan the ease with which he makes his plans seem possible.

" barry's great strength is that he's always been able to take highly complex ideas and make them understood, without prostituting the idea," says Don Rose, community activist and manager of Jane Byrne's successful campaign for mayor of Chicago. (Rose is a force along with Commoner in the Citizen's Committee to form a new political party.)

Critics, however, charge that Commoner ignores work being done in this country on alternate sources of energy, ignores the cost and unworkability of some ideas and gives simplistic answers to complex, convoluted problems. A massive shift to gasohol would raise food prices and cause food shortages, says one. "There isn't that much arable land to turn a fourth of it, say, into producing crops for energy purposes."

Commoner dismisses such talk. "There's just a lot of mythology" (regarding gasohol). "I finally just got a Department of Energy grant to develop ways of intergrating alcohol and methane production into Midwestern cornbelt agriculture. This could have been done two, three years ago."

A DOE spokesman says, "Commoner has played a terribly important role, but now he's shriller, far more intolerant and less informed. He's forgotten Aldous Huxley's first rule: Facts don't cease to exist just because you choose to ignore them."

Commoner's emphasis on relevance has led him not just to alternate sources of energy but to alternate sources of political parties. "I want to make this clear. We are not talking about a third party. We think of this as analagous to the creation of the Republican Party before the Civil War when the two parties were incapable of dealing with the basic issue, slavery. The Republican Party really forced that issue into politics - and in the end, replaced the Whigs."

The "Citizen's Party" is sort of in the "parlor radical" stage; its formation will be announced on August 1.

Backers talk of a January 1980 convention to organize the party and another convention in August 1980 to select a candidate for the national presidential campaign.

Commoner is accorded hero status by his followers who surround him after speeches.

At a recent Washington seminar, Commoner demurs when a young "nonuke" advocate with backpack and beard approaches, eyes shining, and says he'll do anything to push Commoner's candidacy.

An auto worker follows. "I admire you so much. Now Dough Fraser [president of the United Auto Workers] is a wonderful guy but he's staying 'quiet on Carter.' Well, I'm with Buick. We make the big cars and thousands are going to be unemployed. I'm glad you're speaking out. A lot of people ridiculed you on solar. I think they're wrong."

Commoner gives a definite seconding opinion: "They are wrong."

Commoner is unperturbed by the many who scoff at the possibility of forming a party strong enough to replace the current political system.

Commoner - the man who has warned for 25 years that simply living in the 20th century can be hazardous to your health - is in the long run, he says, learning on a well-worn but suitable cliche, "an incurable optimist." CAPTION: Picture, Barry Commoner: by Harry Naltchayan - The Washington Post