WASHINGTON (Reuters) - Richard Perle, an architect of the U.S.-led war on Iraq, offered to resign as chairman of a Pentagon advisory panel, according to a letter obtained by Reuters on Thursday. Noting criticism of a possible conflict of interest over his roles as corporate adviser and Defense Department consultant, Perle wrote to Defense Secretary Donald Rumsfeld, "As I cannot quickly or easily quell criticism of me based on errors of fact concerning my activities, the least I can do under these circumstances is to ask you to accept my resignation as chairman of the Defense Policy Board."