He may be only 44 days old, but William Arthur Philip Louis, otherwise known as Prince William of Wales, already knows how to behave with royal decorum when the occasion demands. During his christening today in the ivory and gold splendor of Buckingham Palace's Music Room, he let out only three small cries as the archbishop of Canterbury, Dr. Robert Runcie, poured baptismal water over the royal forehead.

It was a family affair, with just 60 guests witnessing the young prince's impeccable performance, including Queen Elizabeth and Prince Philip as well as the princess of Wales' father Earl Spencer, her stepmother Raine and her mother Mrs. Frances Shand-Kydd. It was the first time the earl's first and second wives had met since the royal wedding just over a year ago. Also present were two proud great-grandmothers--Queen Elizabeth, the queen mother, and Diana's grandmother, Lady Fermoy. It was a double celebration for Britain's beloved "Queen Mum" since the christening date had been chosen to coincide with her 82nd birthday.

The only members of the immediate family not present were the queen's second son, Prince Andrew, still on helicopter duty with the Falkland Islands task force, and her sister, Princess Margaret, who is on holiday in Italy. London's daily tabloids gave critical prominence to the princess' absence. One quoted her spokesman as saying: "The christening of your nephew's child is not the most important occasion in the year."

The ceremony lasted just 25 minutes and was the first royal christening for the archbishop of Canterbury. He used water flown in from the River Jordan and a 19th-century silver gilt lily font which is normally kept in the Tower of London as part of the crown jewels.

The prince was named William because his parents liked it, Arthur because it is one of his father's names, Philip after his grandfather, the duke of Edinburgh, and Louis after Prince Charles' beloved great-uncle, the late Earl Mountbatten of Burma.

Prince William wore the same gown that his father, Prince Charles, wore more than 33 years ago when he was christened in the same room. Made of fine lace and lined in white satin, the gown also was worn by the queen, King George VI and King Edward VII at their baptisms.

Once the formalities were over, Britain's tiniest royal was not about to stand on ceremony for the army of photographers bent on recording the occasion for posterity. He grumbled as soon as the first bulb flashed and from then on his irritation rose. He insisted on sucking his mother's little finger and screamed every time it was removed. No other finger would do. Both the queen and the queen mother had theirs angrily rejected. "He's a good speechmaker," remarked the queen.

The princess of Wales, who looked radiant but flustered in a pink, blue and white floral dress and a pink wide-brimmed hat, blushed with embarrassment every time her small son made his displeasure known. Everyone tried to comfort him. His father, obviously well-trained in the art of baby care, produced a royal handkerchief to wipe a moist chin. Even Aunt Anne, not known especially for her ability to win people over, made a few clucking noises--but she was ignored.

"He's certainly got a good set of lungs," commented the queen mother, who was left holding the baby at the end of the photographic session. Balancing the baby was no problem for the sprightly octogenarian, unlike her royal predecessor, Queen Victoria. When Victoria posed for pictures with her first grandchild at the end of the last century, there were such fears that she might drop the child that a servant hid under her skirts--supporting the baby with her hands but out of sight of the photographers.

Most female guests at the christnening today stuck to tradition and wore blue for a boy. The queen was in periwinkle blue with white spots, the queen mother in pale blue chiffon and Princess Anne in violet, blue and white. The princess' mother and grandmother were both decked out in blue, and only the three godmothers failed to conform. Princess Alexandra, the queen's cousin, wore yellow and white, and Lady Susan Hussey was in pink. The third godmother, the duchess of Westminster, a close friend of the princess of Wales, wore a white dress--but with blue trimmings.

After the photographers had left, the guests retired to the Blue Drawing Room to toast the baby's health with champagne and settle down to a three-course lunch. This included cutting the christening cake--a layer of the royal wedding cake that was kept for the occasion.

Prince William was not present for these festivities. It had been the most tiring day to date for the future king, and he opted for a simple meal with nanny in the peace and quiet of the nursery.