LONDON.- An eagerly awaited announcement is expected today that Charles Saumarez Smith, current director of the National Portrait Gallery, will become the next director of the National Gallery. Nobody is awaiting it more eagerly than the man himself, who insisted that he had no idea what was going on. "I have made several efforts to find out - but with no success," he said. A spokeswoman for the National Gallery said: "A meeting has been held, and we are expecting to make an announcement this week - possibly today." The National Gallery trustees met on Friday, and are believed to have chosen Mr. Saumarez Smith as successor to Neil McGregor for the top jobs in British galleries, over the inside candidate, Renaissance art expert Nicholas Penny. His appointment must be confirmed by the government before the announcement is made. Both men have been spectacularly successful.