First Lady Barbara Bush spent part of her 65th birthday yesterday reading "Leo the Late Bloomer" by Robert Kraus to a dozen children on ABC-TV's "Good Morning America." The book is about a lion that was slow in learning to read and write -- an appropriate selection, as literacy is Mrs. Bush's most salient cause. When she finished, the children responded with a chorus of "Happy birthday, Mrs. Bush!" "Oh, how'd you know?" she asked. "Who told you that secret?" (On Thursday, Mrs. Bush said she couldn't care less about her birthday.) Later, Mrs. Bush read to a group of children at a District Heights library.

President Bush, meanwhile, was off on a tour of the Midwest, giving speeches and fund-raising. At a luncheon in Omaha, he told his audience, "I wish that Barbara were here on her birthday. ... I'm very, very proud of her, the hero of Wellesley." He was, of course, referring to his wife's triumphant commencement speech last weekend at Wellesley College, where the choice of Mrs. Bush as a speaker had raised a controversy when some students complained she was chosen solely on the basis of her husband's achievements.

The president said he called his wife early yesterday morning and "she seemed unexcited" about turning 65. After receiving a box of pork chops and several bags of pork rinds -- one of his favorite snacks -- from the National Pork Producers' Council, Bush quipped, "Maybe that's what I'll give to Barbara for her birthday present." A Pearl of a Welcome

And speaking of presidential events, Grand Ole Opry humorist Minnie Pearl said Thursday that her trademark "howdee" will greet President Bush and other world leaders during a country music show next month in Houston, on the eve of the economic summit. "I want to say how proud I'll be to say 'howdee,' " she said. Surely the leaders of the United States, Japan, West Germany, Britain, France, Italy and Canada, who've met annually since 1975, can hardly wait. Other celebrities scheduled to perform at the show include singers Loretta Lynn, Charley Pride and Larry Gatlin and the Gatlin Brothers. Makarova's Latest Step

The American Ballet Theatre has announced that its new artistic adviser will be Natalia Makarova. "I have considered American Ballet Theatre my home since I left Russia in 1970," she said Thursday. "I am happy to now be reassociated with ABT, and look forward to passing on my knowledge and artistic experience." Makarova made her ABT debut in 1970 in "Giselle" and spent 15 years as a ballerina in the company. No one has been named as artistic director since Mikhail Baryshnikov's resignation last September.

Madonna's Downtown Stop

She may be blond -- this week. She may be ambitious -- always. But Madonna is definitely not one to stiff the waiter. So says Savino Recine, owner of downtown's Primi Piatti restaurant. Recine reports that the platinum bombshell and three friends -- one woman and two men -- had supper there around 8:30 Thursday, the night before her first concert at Capital Centre. "She had a very light dinner," the restaurateur said. "A little pasta and some green vegetables." He said Madonna sat in the non-smoking section, wore a miniskirt and caused several heads to turn. She turned down champagne and requests for autographs, but not "Pastas and Risotto," an educational cooking video featuring Recine and his chef and assistant chef. Recine's overall impression of the Material Girl? "Very pleasant. And she left a good tip."