Nothing changes the mood of your midweek Washington party like a few country music stars, who sing about love, despair and cheating men, and therefore, see life as it really is. Take Charly McClain. She arrived at a reception after performing in the Country Music Association's concert at Constitution Hall last night and announced:

"I'm desperate. I'm trying to find a husband."

Jeff Cook, of the country group Alabama, promptly asked for her phone number.

"But you're married, aren't you?" asked McClain.

"Not in this state," said Cook.

Everybody laughed, but McClain, who was wearing a black mini-dress and red pumps, was insistent.

"I want to get married in two or three years," she said. "I really do. I thought I met someone a few months ago, but he ended up like everyone else. That's the problem with this business. After 25 days on the road, one-nighters, affairs, I'm tired."

At this point, Lee Atwater, from the White House political office, wandered up.

"You were excellent," he said, complimenting McClain on her singing.

"You remembered me?" she said, brightening.

"Not only do I remember," said Atwater, "but I particularly remember you."

"What was I wearing?" she asked.

He didn't remember.

And so the evening went. Ronald and Nancy Reagan, George and Barbara Bush and a good 2,500 people from Washington's social, political and journalistic high order turned up for the Country Music Association's 25th anniversary concert, taped at Constitution Hall for broadcast on CBS April 13. Almost 40 country music stars were there, including:

Charlie Daniels, Loretta Lynn, Barbara Mandrell, Charley Pride, Ray Charles, Ronnie Milsap, Minnie Pearl, Jimmy Dean, Glen Campbell, Brenda Lee, Tammy Wynette, Mickey Gilley, Larry Gatlin and more--including Willie Nelson, who played "On the Road Again," a clear Washington hit.

Nelson is always the artist identified with Jimmy Carter, although "On the Road Again" was first the theme song for the Reagan campaign plane, then was picked up on the Carter plane in the final weeks of the campaign, and now is being played on Sen. Alan Cranston's (D-Calif.) presidential campaign flights. They fiddled and sang for 2 1/2 hours, and afterward, shook hands with Reagan.

"There was only one unsettling thing," Reagan said from the stage, where he looked perfectly at home amid the two score of entertainers. "Every time they talked about fiddling, I thought another congressional committee was messing around with the defense budget." Everyone laughed heartily.

"But if there was ever a night to forget your cares," Reagan added, "this was it."

For Washingtonians it was also an evening to see how a television show is really taped. Several times the crowd had to applaud an act twice--once for the real thing, the second time for the television cameras. "We gotta applaud right now like Mickey Gilley and Carl Perkins just finished," John ("Dukes of Hazzard") Schneider told the crowd. "Weren't they great?"

And at that, 2,500 dutifully followed instructions and clapped.

Among those getting a hand were Senate Minority Leader Robert C. Byrd (D-W.Va.), who fiddled, and Senate Majority Leader Howard H. Baker Jr. (R-Tenn.), who talked about his roots.

Gilley came to the reception afterward, wearing what he estimated was $90,000 in diamond jewelry. He had on three diamond rings (one alone had 84 diamonds in it) and a diamond necklace with his initials. Gilley is the guy who owned the bar in the movie and magazine article "Urban Cowboy" that writer Aaron Latham made famous. Latham is married to CBS White House correspondent Lesley Stahl, which brings this full circle or at least shows that there are only 175 people in the world.

Yesterday, Stahl and Latham took Gilley to the White House, where deputy press secretary Larry Speakes (who once played in a country band, although he won't tell the name) introduced him at the daily press briefing.

"I don't know whether Aaron made Mickey--or Mickey made Aaron," Speakes said at the briefing. Then he and Atwater took Charlie Daniels to lunch in the White House mess. "Daniels has lost 40 pounds," said Speakes. "He ate a salad and had a cup of tea." And last night at the reception, Speakes was beaming. "I've seen kings and queens and presidents," he said, "but I'd rather see country music stars."

But at this particular reception, there weren't too many around. Several hundred Washingtonians, raving about the concert and eager to see Barbara Mandrell and the others close up, piled into the Daughters of the American Revolution museum at Constitution Hall for a look. But the stars were retaping the opening number of the show, which had been fouled up on camera.

But members of Alabama were there. Mark Herndon, who wore black leather pants, said the reason the group hadn't performed last night was that "we had a sex change operation." In fact, they had taped their song the night before.

Meanwhile, Jeff Cook revealed a secret desire:

"I would love to be in the Secret Service."