WASHINGTON – Laura Bush’s knack for comedy may have been the best-kept secret in Washington. It turns out that the former librarian, the sweet smiling political wife, can let loose one-liners with the timing of a stand-up comic.

Her popularity doubles his, so why not let the first lady take over for President Bush in a huge ballroom packed with journalists, a Who’s Who in Washington, and a smattering of Hollywood types? At the 91st annual White House Correspondents’ Association dinner on Saturday night, the president was toasted, but his wife stole the show.

Mrs. Bush was extra cautious before her husband’s re-election not to say or do anything that might hurt his chances for another four years. Her remarks were on-message, her interviews a bit bland.

Since November, she’s been stepping out in more public ways. She launched an initiative that urges at risk children to shun gangs and drugs and avoid making dead-end choices. She took a solo trip to the dangerous Afghanistan capital of Kabul, where her transport helicopter was shadowed by protective Apache attack helicopters. Last week, she was in Burbank, Calif., making her fourth appearance on the “Tonight Show.”

The first lady’s approval rating hovered around 80% in February, according to a USA Today/CNN/Gallup Poll, the most recent measure of her popularity. By contrast, the president’s overall approval rating is at 47%, a Washington Post-ABC News poll released last week shows.

“Tonight Show” host Jay Leno asked her if she ever teases the president about his lower approval ratings.

“No, but I might,” she told Mr. Leno.

It wasn’t the first time a first lady was a showstopper on stage. Shedding her aloof image, Nancy Reagan took center stage at the Washington press’s annual Gridiron Club dinner in 1982. Mocking criticism of her expensive tastes, Mrs. Reagan stepped out in an outlandish Hawaiian print dress with polka dot sleeves and yellow galoshes and sang a self-effacing “Second Hand Clothes” to the tune of “Second Hand Rose.”

Mrs. Bush’s audience at the White House correspondents’ dinner assumed they’d be hearing another speech from the president. But giving her the mike was the plan all along. Just as he launched into some cowboy yarn about a city slicker, Mrs. Bush got up, walked up from behind him and exclaimed, “Not that old joke, not again.”

She said she had sat patiently long enough, that she had a few things she wanted to say, and then went on to roast the president, starting off with his early bedtime.

“Here’s our typical evening: Nine o’clock: Mr. Excitement here is sound asleep,” Mrs. Bush said. “I’m watching ‘Desperate Housewives’ with Lynne Cheney. Ladies and gentlemen, I am a desperate housewife. I mean, if those women on that show think they’re desperate, they oughta be with George.”

It was one one-liner after another.

After ripping her husband, she went on to roast Vice President Cheney, two Supreme Court justices, and Defense Secretary Rumsfeld. She talked about how Mr. Bush often cleared brush and cut down trees at the ranch – something their twin daughters call the “Texas Chainsaw Massacre.”

“George’s answer to any problem at the ranch is to cut it down with a chain saw, which, I think, is why he and Cheney and Rumsfeld get along so well,” she said.