Boston does not bake a 15-foot cake for just any occasion. Beginning at noon today, an estimated 5000-10,000 citizens will gather in City Hall Plaza to gaze upon the bakery masterpiece and join the festivities surrounding the city's 350th birthday. Robert Burke '73, one of the organizers of "Boston Jubilee 350," said yesterday.

Throughout the afternoon, musical groups--including the Spring Revels and the New England Conservatory Jazz Band--will provide live entertainment. Three hot-air balloons will offer a preview of the full-scale balloon race over the weekend. Boston Mayor Kevin C. White will cut the cake, opening the reception center for the celebration.

At the center of the revels will be the cake--handiwork of Arthur Strasnick. Weighing 7-8000 pounds, the cake is eight feet long as has 11 tiers. Although the cake is vanilla-flavored, Strasnick has decorated the cake in red, white, and blue and added pictures of scenes from Boston's history.

Strasnick has spent three or four days putting the pieces of the cake together--it had to be baked in sections. Three electrical fountains will spout water over it.