Ralph Nader, the consumer advocate who often boasts that his activities have been financed primarily by small contributors, has decided to go after the big money.

To celebrate the 10th anniversary of his research and lobbying arm, Public Citizen, Nader has decided to borrow a page from the rich political candidates and fat-cat fund-raisers he has repeatedly criticized by throwing a $1,000-a-plate dinner Sept. 26 at the Shoreham.

Featuring Hollywood celebrities Ed Asner, Steve Allen and Marlo Thomas, the dinner is being held to raise more than $500,000 for a building to house Nader's corporate empire.

"This is literally the first time we have ever asked people to give more than the usual $15 to $20," said Sidney Wolfe, director of Public Citizen. "Other organizations do this all the time. Maybe we should have, but we haven't," Wolfe added. Nader was out of town and referred all questions to Wolfe.

"It's not a change in terms of our outlook," Wolfe said. "What we would like to do is to be able to have our own building so we will not be gradually squeezed out of the real estate market. Now, our rents are gradually being pushed up; at some point in the future we will literally not be able to afford them."

Originally, the Nader group set a goal of $1 million for the fund-raiser, which caps a two-day conference on consumer issues. But it has since lowered its sights. "A million is our goal, but my expectation is about $500,000," said Beverly Orr, who is in charge of organizing the dinner.

For the dinner, Nader has mailed 4,000 hand-signed, two-page invitations. Many of the letters went to Nader's "large donors" who in the past have contributed $50 or more a year to Public Citizen or Nader's Center for Study of Responsive Law.

From lists drawn up by Nader employes, Nader also sent letters to lawyers, publicists and other individuals who were considered likely candidates to shell out $1,000 for the dinner.

Two hundred corporations were also invited, but they are only those that supported Nader's unsuccessful campaign to get Congress to pass legislation creating a Consumer Protection Agency. These companies include Montgomery Ward, Drug Fair, Giant Food, Levi Strauss and Hallmark Cards.

But corporations that have been criticized by Nader, such as the auto manufacturers, have not been invited.

"We probably would not let them come at all," said Wolfe. The corporations that have been invited were those "who were united with us in the fight for a Consumer Protection Agency -- that's the sort of company we would try to get a contribution from."

All this doesn't seem to bother the uninvited, especially General Motors, the corporate giant Nader first took on. "Unfortunately with the current high interest rates and spotty auto sales, we're having to turn down all such opportunities at this time," R.T. Kingman Jr., public relations director for the Washington office of General Motors, commented.

But while the $1,000 dinner is a break with tradition, Nader is not planning to change all of the rules that have governed his activities. The dinner will not be black tie. "That would not be like Public Citizen," said Wolfe.