Just when you think Washington has plumb run out of honored guests for its plethora of fund-raising events, organizers resort to -- well, a little make-believe.

Last night, at the Seventh Annual Ambassadors Ball to raise money for the National Multiple Sclerosis Society, Mickey Mouse, Pluto, Snow White and several of their friends turned the usually staid Washington audience giddy when they skipped on stage at the Washington Hilton.

The Disney characters were flown north from Disney World, gratis, for what has become one of Washington's more lucrative fund-raising events. At $150 per ticket for a dinner completely underwritten by Philip Morris International, the National Multiple Sclerosis Society expected to raise nearly $300,000.

Among the guests were Jihan Sadat, U.N. Secretary General Javier Pe'rez de Cue'llar, Attorney General Edwin Meese and Ursula Meese, Agriculture Secretary John Block, White House counsel Fred Fielding, Interior Secretary Donald Hodel and ambassadors from just about every country.

Here's what some of them had to say about President Reagan's sanctions against South Africa:

"I think it's tokenism," said Botswana Ambassador Serara Ketlogetswe.

"Sanctions are pressure, and any pressure is good pressure," said Irish Ambassador Patrick MacKernan. "It's a step in the right direction."

"I think it's a good beginning, but it is not enough," said Algerian Ambassador Mohamed Sahnoun. "The sanctions need to be more comprehensive."

Sadat, who is currently teaching a course about the status of women in the Mideast at the University of South Carolina, said last night that she hopes to be finished writing her autobiography by next year.

"I hope my story will be an inspiration to all women," she said.

The fun started after the last bite of raspberry sorbet, when Mickey and Minnie appeared to much applause. Another dozen storybook favorites jumped into the audience and charmed the crowd with their dancing and prancing. They sang the song the 1964 New York World's Fair made famous: "It's a Small World ."

Afterward, the true believers came forward for what can best described as a photo opportunity with the Disney character of their choice.

"I'd like to have my picture taken with Alice in Wonderland," said Fielding. "In Washington, I think that's only appropriate."