Supreme Court nominee David Souter had a big day Monday, celebrating his 51st birthday while concluding his testimony to the Senate Judiciary Committee in his confirmation hearings. He celebrated afterward with a filet mignon dinner at the Palm restaurant, joined by his friends Sen. Warren Rudman (R-N.H.), White House Congressional Liaison Fred McClure, New Hampshire lawyer Thomas Rath, political consultant and former Reagan chief of staff Kenneth Duberstein and Duberstein associate Michael Berman. For dessert, the waiter brought over a slice of cheesecake topped with a single candle while the restaurant staff gathered around and sang "Happy birthday, dear Davey."

The Cronkite Chronicles Twenty years ago Walter Cronkite signed a contract with Alfred A. Knopf Inc. to write his autobiography. This summer he finally began work on the project, the former CBS News anchor admits in the Sept. 24 issue of People magazine. While the writing is coming along smoothly, he is worried about finding a title. "I'm going to have to fight the publishers to keep them from calling it 'And That's the Way It Is.' "

No Clue in Violinist's Case The case of the violinist who submitted an apparently phony audition tape remains unsolved, but a winner has been named in the International Violin Competition of Indianapolis. Top honors went to 20-year-old Soviet violinist Pavel Berman, who won a gold medal, $20,000 in cash, a recording contract and more than 50 concert dates including a Carnegie Hall debut. Pavel is the son of pianist Lazar Berman, who created a sensation when he first toured the United States in the early 1970s.

The competition made the headlines earlier this month when one audition tape bore the unmistakable notes of a master -- unfortunately, apparently not those of the contestant who submitted it. Some experts at the competition said they thought the audition tape was actually the work of Fritz Kreisler or Yehudi Menuhin, but no final answer was reached.

The highest-scoring American, among the 52 contestants who had been picked from nearly 200 applicants, was Ivan Chan, 23, who came in third, winning a bronze medal and $10,000 in cash. Second place and $15,000 went to Marco Rizzi of Italy.

No to USO Show The Marine Corps' top brass yesterday criticized as "ludicrous" USO plans to provide a little diversion in the desert for U.S. troops.

Gen. Al Gray, the blunt-spoken Marine commandant, said the entertainment organized by the United Service Organization, which has booked comedians Steve Martin and Jay Leno and is wooing other big-name talent to perform for the more than 150,000 American troops deployed in the Persian Gulf area, "detracts from the mission at hand." Martin is scheduled to go to Saudi Arabia next month to meet with soldiers at an air base in the northeastern Saudi city of Dhahran.

"We shouldn't be having any shows over there," Gray told a small group of reporters in an impromptu conversation at Camp Lejeune, N.C. "That's ludicrous. Common sense will tell you" that such entertainment is inappropriate, he said.

Cher's Tea and Sympathies Barbara Bush plays teatime host today to an unusual White House visitor: Cher. Not to worry, though, the First Lady and the entertainer aren't likely to be talking tattoos. Instead, they'll chat about something they do have in common -- a commitment to helping children.

Cher is in Washington attending several benefits for the International Craniofacial Foundation, an organization she became involved with after doing the 1985 film "Mask," playing the mother of a teenage boy whose face was deformed. The pop-movie star will also meet with the new Soviet ambassador, Alexander Bessmertnykh, and attend a fund-raising auction with actor Stacy Keach, appearing at the Folger as Richard III.

Ruckus on Radar The governor of North Dakota, George Sinner, has a radar detector on the dashboard of his truck, a fact that has caused a ruckus in Bismarck. Republican state Sen. Bryce Streibel, a frequent critic of the Democratic governor, said, "That's a heck of an example to set. You've got a fuzzbuster in your car for one reason and that's to evade the law." Though the devices are legal in North Dakota, Sinner admits to appearing a tad hypocritical in using one. He says it was a gift from his children during his first campaign for governor, calling it a "sacred, emotional thing." Streibel wasn't moved by the plea: "Hold on. Let me get my handkerchief."

Chuck Conconi has the day off.