The president admitted that he was prejudiced and nobody in the crowd of 1,150 could have doubted it for a minute.

"In my judgment," Jimmy Carter said, "you have chosen someone who could not be a better person to exemplify . . ."

"Hear, hear," interrupted a voice from the floor.

"You've chosen," the president began again, "a person that I love more than anyone else in the world -- not only because of her personal relationship with me but because of what I know she means to other people."

So it went last night at the Shoreham Hotel as the National Mental Health Association (NMHA) and the District of Columbia Mental Health Association combined to salute Rosalynn Carter as "volunteer of the decade" for her work in the field of mental health.

"A milestone in mental health history," said Beverly Benson Long of Atlanta, president of the 1-million member national organization which went big-time in fund-raising this year for the first time in its 77-year history when it hired a national director of resource development.

We're really amateurs," said Barbara M. Stockton, president of the D.C. assocation which will split proceeds of last night's dinner, an estimated $140,000 after expenses.

Billed as a "bipartisan" event which supposedly drew support from both parties in Congress, the dinner had a turnout rich with patrons and sponsors outside government. There in force -- and black tie -- were big spenders from such trades and industries as oil, construction, pharmaceuticals, insurance, electronics, food and communications. In additon there were representatives from several unions.

"A complete sell-out," said Pamela Harriman, who co-chaired the dinner with her husband Averell. It was a response, she said, that gave people a chance, "to say thank you to Mrs. Carter that had nothing to do with politics."

Still, Washington being Washington, politics somehow managed to sneak into the festivities anyway. Besides Averell Harriman, a kind of Moses in residence of the Democratic Party here, present -- and accounting for it -- were Joan Mondale, wife of the vice president; Secretary of Health and Human Resources Patricia Harris, and Mayor Marion Barry.

Barry's pitch was D.C. representation in Congress. Pat Harris urged enactment of the Mental Health Systems Act now before Congress.And Joan Mondale, honorary chairperson for the evening, stumped for the Carters. j

"Rosalynn and Jimmy Carter have gone a long way toward returning the presidency to the people of the United States," said Joan Mondale.

And in defining Rosalynn Carter's interpretation of her role as first lady, Mondale sketched what she called "the two schools" of thought about what Americans expect of first ladies. One is the "ornamental school," meaning to be seen but not heard from. The other is "the school of extreme usefulness" and judges a first lady by how tired she is at the end of the day.

"She is inevitably criticized for being too involved in politics or not enough, for advising her husband too much or not enough," said Joan Mondale. "Rosalynn has a happy solution, though; she ignores it and insists upon being herself."

When the president arrived (he had changed into his tuxedo aboard Air Force One, he said) some people probably thought he was going to talk politics like everybody else. He didn't disappoint them, though his remarks were as much about voluteerism as his meetings with angry blacks in Miami, mayors in Seattle and tornado victims in Grand Island.

"There can be no higher honor, in my judgment," he said, without mentioning any names, "than to call someone a volunteer."

When he went back to his chair, he had a big kiss for the "volunteer of the decade." Rosalynn Carter later told the audience that "I should be the one who is honoring you because you have worked so long, persevered so long to make the Mental Health Association the effective force it is today."

The idea for a fund-raiser caught fire last winter, according to Lewis A. Strudler, NMHA director for resource development, when Rosalynn Carter gave it her blessing. Three months ago the White House okayed the date. Initially, the goal was to sell 50 tables but by last night 95 had been bought at prices staring at $150 and climbing to $2,500 for tables of 10.

"We could have sold an additional 20 tables," said Strudler.