A former president of Milpitas-based California Micro Devices Corp. has pleaded guilty to securities fraud at the start of his trial, prompting a federal judge to declare a mistrial against two other executives. Surendra Gupta was one of several former Cal Micro executives accused of inflating the company's revenue statements to boost stock prices. The former chief accounting officer, Ronald Romito, pleaded guilty to insider trading in December 1995. Gupta pleaded guilty to securities fraud and conspiracy. He also said the other two defendants--Chan Desaigoudar, former chairman and chief executive, and Steven J. Henke, former vice president, treasurer and chief financial officer--were involved in planning and carrying out the fraud. Lawyers for Desaigoudar and Henke asked for a mistrial, saying Gupta's sudden absence from the defense table could have an unfair effect on the jury. U.S. District Judge Vaughn Walker granted the request.