They played the Tennessee Waltz for Howard Baker last night, waved enough red, white and blue placards to paper the Republican National Convention and heard Mr. Grand Ole Opry himself.

And from the looks of all the political hoopla and hyperbole, you'd have thought all 2,000 of them had an elephant by the tail.

"Later on," said Roy Acuff, the "king" of country music and yo-yo coach of presidents, "I'll come up and teach Howard Baker how to yo-yo at the White House."

If anybody could, it would probably be Acuff -- who once captivated a national TV audience by giving Richard Nixon yo-yo lessons onstage at the Opry.

There was no yo-yo last night, however, only a highly charged crowd jammed into the ballroom at L'Enfant Plaza Hotel for a first look at the Tennessee senator after he made it official yesterday that he's a candidate for the Republican presidential nomination.

"The enthusiasm of the crowd tonight is proof already that in November 1980, we're going to have the biggest victory the Republican party has had in 30 years," Baker told the crowd.

Bobbing up almost as if by orchestration were dozens of placards proclaiming everything from "New York for Baker" and "Connecticut for Baker" to "Volunteers for Baker" and "Howard Baker -- He Can Cross Any Bridge."

"We'll have this party again in January 1981 -- in the White House," Baker promised, seeding the crowd into paroxysms of glee.

About 25,000 invitations went out around the country but most of the 2,000 who showed up came from nearby states and from Tennessee. Many were longtime Baker fans, some were new converts and a few were frankly "shopping."

"Come on," said one young veteran of Washington parties, "how many invitations do you get that cost $125. This one was free."

The old guard of establishment Washington wasn't in evidence but a young guard, mostly under 30, bore out what Baker aides maintain is a strong appeal to youth. It is no accident, Tom Griscom, Baker's compaign press secretary indicated, that the candidate's first campaign stop today will be at Brown University.

"Baker's organization is underestimated," said Kent Smith of Wilmington, Del., "and the emphasis on leadership is intended to attract young leadership. The old guard is committed to Connally and Reagan."

Debbie Clark of Vienna, Va., said that when her husband (a Democrat) began talking about Baker, she decided to take a look.

"I started reading his positions on issues and I thought, 'that's what I think, too.'"

Steve Martindale, Washington's lawyer-about-town, said he attended Baker's announcement, went to the lunch later and gave him $1,000. But he was hedging his bets, too.

"I'm also going to do everything I can for Teddy Kennedy. I love Joan and I love Teddy -- they're close friends of mine. I'm just sorry Carter hasn't been an effective administrator because this country needs someone in the White House who is."

Baker's campaign manager, Indiana Sen. Richard Lugar, said Baker's determination to defeat SALT II if it does not include certain amendments was unrelated to appeasing his Panama Canal critics.

"I think there are different constituencies. The broader constituency is concerned about national defense. The Panama Canal issue was important but if you're going to take on somebody, you take on the Soviets."

Who does Baker think he might take on among the Democrats should he win the GOP nomination? "Hard to tell," he said as he, his wife, Joy, and others in the entourage waited for their limousines to pick them up.

"Too early to count Carter out, too soon to know how good a campaigner Kennedy will be. Anyway," he said, "I've got my hands full with the Republicans right now."