After a week of the royal family's private deliberations whetting the most intense of public curiosity, Buckingham Palace announced today that the newborn son of Charles and Diana, the Prince and Princess of Wales, will be named William Arthur Philip Louis.

For now the baby's official title is Prince William of Wales. Someday, assuming all goes according to plan, he'll become Britain's fifth King William, the first by that name since 1837.

From the instant last Monday evening that Diana, in the presence of her husband Charles, bore a son, Britain has been in the grip of babymania. Poems, paeans of one kind and another, contests, solemn advice and knickknacks have poured forth in commemoration of what is clearly regarded by many British as a truly blessed event.

With each passing day, the name game became more frenetic. It would be Oliver, a name that Diana for some reason particularly liked, several newspapers reported. Others said it would defintely be Stephen, a more contemporary moniker. Bookmakers took odds on George, Arthur, Albert, Louis and James. William was the late favorite at 7 to 2. The long shots, quoted at 1,000 to 1, were Elvis, Bjorn and Canute.

Buckingham Palace's announcement offered no explanation of why William was chosen. Harold Brooks-Baker, the royal genealogist, said Charles and Diana had been traditional "but not too traditional" in their selection. He reckoned that William was the least likely of fully "accepted" names. "It seems clear that William was Diana's choice," Brooks-Baker said. "She is a woman of decision and strong will, who is likely to have her way on all matters on which she feels strongly."

As for the other names, to keep track (and it isn't easy), remember that the Prince of Wales' full name is Charles Philip Arthur George. His son has been given two of those: Philip, the name of Charles' father, the Prince of Edinburgh; and Arthur, a legendary English king. Louis was a name widely favored because of Charles' attachment to Lord Louis Mountbatten, his great uncle and a family favorite who was killed by a terrorist bomb in 1978.

When Prince William does come to reign, the choice will be his whether he wants to stick with that name or opt for something else. The likelihood, royal experts said, based on the record, is that he'll stay with William. The first William, it is noted, was an especially celebrated monarch who, as the Duke of Normandy, captured England in 1066 and was known, therefore, as William the Conqueror.

Margaret Brown of York, who as a hobby keeps track of birth announcements in the London Times and compiles lists of names, ranking them by popularity, said today that William is now tied for fourth with Alexander. They follow James, Thomas and Edward. Selection of a name by one of the royals, Brown said, always increases the popularity of that name for a time.

"Peter went up slightly in popularity after Princess Anne called her son Peter," she said, "and I suppose with this prince the name will be even more influential."

At the moment, nothing Charles' sister Princess Anne does can add to her sagging popularity. She has provided the only sour notes in the national jubilation over the baby and has been widely criticized in the press. On a trip to the American West last week, she sneered at reporters who asked her how she felt about the birth of her nephew, replying, "That's my business, thank you very much" and striding away. Later, Anne agreed with a reporter's observation that "too much fuss" was being made about the birth. "Anne Rapped by Queen," the tabloid Sun headlined on an exclusive account of the dressing-down Queen Elizabeth gave her testy daughter.

Others newspapers pointed out, as the British tend to do when piqued at a member of royalty, that Anne is highly paid to be gracious--something like $3,700 a week plus perquisites--and should be expected to show couth when neccesary.

But for Charles and Diana, there is only adoration. The Times of London struck a thoughtful note by recalling the words of British scholar Walter Bagehot a hundred years ago: "A royal family sweetens politics by the reasonable addition of nice and pretty events. It introduces irrelevant facts into the business of government, but they are facts which speak to men's bosoms." Others observed that young William could well be reigning over Britain well into the second half of the 21st century--the sort of long view that gives people a sense of royalty's enduring qualities.

Meantime, babies are in vogue here. There are contests for the "bonniest" baby, and Parliament passed a resolution warmly congratulating the couple. An amendment was added to make the congratulations apply to all babies born last week, but the royal one clearly is very special.

The Daily Telegraph produced "A Nativity Ode" as its lead editorial the day after the royal heir was born. "It went, in part, like this: Diana, once a goddess Worshipped in ancient Rome Is now a Prince's mother, In England, in our home. There she was a chaste huntress, Who as the moon did run: Now in England, in midsummer, From her, there shines a son.