David Cassidy, heartthrob star of the 1970s sitcom The Partridge Family, filed for bankruptcy protection, citing both assets and debt of as much as $10 million, Bloomberg News reported yesterday. Cassidy, who has homes in Florida and Saratoga Springs, N.Y., listed credit card debt including $21,000 owed to American Express and $17,000 owed to Citi bank, among other liabilities, in his chapter 11 petition filed Wednesday in Fort Lauderdale, Florida.