San Francisco socials are atwitter about this potential storm in a teacup: Danielle Steel’s glamorous biannual Star Ball, which benefits the Nick Traina Foundation, has been set for May 1 at the Ritz-Carlton Hotel — as it has been for the past two years. And Steel’s power pack-pals like Jackie Collins, Joanna and Sydney Poitier, Sharon Osbourne, Tipper Gore and Dame Elizabeth Taylor are set to attend. But, since last fall, social newcomer Tatiana Sorokko has been planning a big 50th birthday party for her art collector husband, Serge, at the Palace of the Legion of Honor on the very same day. Her guests include Georgette Mosbacher, Frank and Karen Caulfield, and Urannia and Brunno Ristow. Naturally, many of the same guests are invited to both parties and are now in a quandary over which invitation to accept. When Steel heard about Sorokko’s party, one source reported that she phoned the former model and asked her to change the date of her birthday party. But Sorokko told her that family members were flying in from around the globe and the date could not be changed. The result? A standoff that has left many of the city’s socials contemplating the age-old escape tactic: leaving town for the weekend.