When 2,300 motorcycle riders convened for their annual get-together, picnic and beer-fest in Menoken, N.D., the last thing they expected was to be lobbied.

But last weekend, blazoned across a giant trough filled with beer kegs, was a two-foot-high sign warning that Congress was considering an increase in the federal tax on beer. Anyone opposed should write Rep. Byron L. Dorgan and protest, the sign said. The address of the North Dakota Democrat's congressional office was helpfully appended.

"I'm flattered by the attention, but I think the campaign is not very smart," Dorgan said. "If those beer folks want to talk to me about their excise taxes, all they have to do is come in and visit. Nor am I pleased to have my name plastered on every beer keg at a bikers' convention."

The sign at the motorcycle bash represents the latest version of a familiar Washington institution: fighting a legislative battle by persuading average Americans to side with whatever industry group is under siege. As Congress sets out to raise $19 billion in revenue, the beer, wine, liquor, tobacco, trucking and telephone industries have undertaken a massive grass-roots lobbying campaign to forestall increases in excise taxes.

Already, before a single hearing has been held or a single proposal considered, the effort has spawned four studies on the impact of higher excise taxes on poor Americans. And it has given rise to three self-styled consumer groups opposed to higher excise taxes, all of them funded in whole or part by industry interests.

They are:

Coalition Against Regressive Taxation (CART), a multi-industry coalition that commissioned a study, bought newspaper ads in the congressional districts of all 36 members of the House Ways and Means Committee and flew hired economists to some 15 cities, where they met with newspaper editorial boards and spoke against excise-tax increases.

Consumers Opposed to Secret Taxes (CO$T), which says it is a "national organization of consumer advocates" and is funded in part by CART. CO$T also commissioned a study, paid for by CART. Like the CART report, it found that higher excise taxes on alcohol, tobacco or gasoline would virtually wipe out this year's tax cuts for low-income taxpayers.

Consumer Alert Advocate Fund, an Illinois-based group in whose name the beer industry has placed full-page, anti-excise ads in 57 newspapers around the country. The group receives contributions from individuals -- and from the telephone, auto and oil industries.

Many of the newspaper ads do not make clear who is paying for them. A full-page advertisement funded by the tobacco industry headlined "Sneak Attax" tells readers that those "hit hardest" by excise taxes are "working Americans -- like factory workers, office workers and family farmers -- the people last year's tax reform bill was supposed to help."

The ad, which ran in eight large newspapers around the country, was paid for by the Tobacco Institute, under the auspices of CART. It urges readers to write their local member of Congress, whose name and address is included in the ad. It lists an address for CART that actually is the Capitol Hill office of the American Trucking Associations, which coordinates CART activities.

Another ad, openly sponsored by the Beer Institute "on behalf of 80 million American beer drinkers," invites readers to call a toll-free number and dictate a message to the operator, who zips it to the proper lawmaker by Western Union. So far, some 20,000 mailgrams have flowed to Capitol Hill offices.

CART also has paid to send two economic consultants around the country to help mold public opinion by making speeches, holding news conferences and meeting with reporters and editorial-page editors. Laurence H. Meyer and Joel Prakken of Laurence H. Meyer and Associates in St. Louis are typically presented to audiences as outside experts on taxes, Meyer said.

Industry groups involved in the lobby effort said that public sentiment against higher excise taxes is genuine and that they are only informing taxpayers of proposals they might not know about otherwise.

"It is democracy in action," said Patricia Bario, whose public-relations firm was "donated" to help CART by one of its clients, Miller Brewing Co. "All we are trying to do is inform the public about what is going on in Congress and let them react any way they would like to."

Some opponents of excise-tax increases see the lobbying effort as a happy confluence of interests. Corporations that can afford expensive advertising and public relations team up with advocates of consumers who cannot afford to pay more for beer, cigarettes or gasoline.

"My general philosophy is, whenever the consumer position coincides with a portion of the industry position, I have no objection to collaborating with them in order to achieve a common goal," said the Rev. Robert J. McEwen, chairman of CO$T and a former president of several consumer organizations. McEwen said he receives no compensation for his appearances around the country to speak against higher excise taxes, but his expenses are paid by CART.