Only Tuesday, the White House Millennium Council and first lady Hillary Rodham Clinton announced who will help Washington and the nation ring in New Year 2000: Will Smith! Aretha Franklin! Chuck Berry! B.B. King!

But yesterday, while not quite singing the blues, organizers were acknowledging an unfortunate--and they hope momentary--mistake. The King of Blues, it turns out, is not yet confirmed for the "America's Millennium" spectacular being planned for the Mall. They want him, and he may be willing, but there's no ink on a contract.

The mixup over King began at Tuesday's news conference, when for the first time in months organizers provided details on the three-day celebration weekend. The trouble was, they weren't specific enough. Because most of the discussion was about the plans for Dec. 31--a show to be hosted by Smith, a made-for-the-millennium movie by Steven Spielberg, a techno-glitzy light display at the stroke of midnight--it seemed that performers such as Berry were set to appear that day, too.

They're not. Mr. Rock-and-Roll is to be on the Mall the afternoon of Jan. 1. The Queen of Soul, who's playing the Jacob Javits Center in New York on New Year's Eve, will not show until Jan. 2. As for King, he has engagements in the Memphis area Dec. 31 and New Year's Day and could arrive in Washington, if and when the glitch is straightened out, only on Jan. 2.

"It was the worst kind of mistake," said Richard Kurin, director of the Smithsonian Institution's Center for Folklife Programs and Cultural Studies, who's heading the planning for the many exhibits, concerts, lectures and demonstrations the Smithsonian intends to put on for those three days. He missed the news conference Tuesday because he was out of town, but much of his day yesterday was spent trying to resolve problems.

Paul McCarthy, executive director of the entity that is trying to coordinate everything among the White House, Smithsonian, National Park Service and National Park Foundation, also was trying to regain lost ground. He lamented that the very thing organizers wanted to avoid--confusion over details--happened.

"We'd prefer to come out with a comprehensive list of all the entertainers and the time slots they're in," he said.

Not surprisingly, much is up in the air because the budget for the free weekend celebration is still so uncertain. The bills will be picked up by private donations, and organizers said this week that they have raised about half of their $12.5 million target. That amount will cover only the events on the Mall, however, not a companion festival on Constitution Avenue that is a cooperative effort with the city.

"What we're trying to do is plan for different levels of programs," Kurin said. "If we don't get that kind of money, we'll scale back."

On the music stage on the Mall--the major draw--Kurin wants Franklin, Berry, former Grateful Dead drummer Mickey Hart and other unannounced performers to do more than play. What if, he mused, they talked about what has influenced them in their music, and how soul or rock might change in the 21st century?

"It would be tres cool," Kurin said.

But with barely 90 days to go, time is growing short for booking other acts and contracting with vendors. The Smithsonian has received less than $1 million through the White House Millennium Council, Kurin said. Despite that, he's hopeful that all three days will be strong draws. "We're negotiating. What can I say?"

The first lady's press office, which is now handling inquiries on the event, said no timetable exists for releasing more information on the celebration. Filmmaker George Stevens Jr. and musician Quincy Jones are producing the Dec. 31 show at the Lincoln Memorial.

And as Stevens said Tuesday, "It's always a great mistake to tell people what you're going to do three months in advance."