* Dr. Benjamin H. Kean, a tropical disease expert who helped discover the cause of traveler's diarrhea and played a disputed role in the Iran hostage crisis as physician to the Shah of Iran, died Friday of colon cancer. He was 81. Dr. Kean reportedly told President Carter in 1979 that the deposed Shah was near death and needed medical treatment in New York. President Carter's decision to let him in the United States led to the storming of the U.S. Embassy in Tehran, Iran, and the seizure of 50 hostages by Muslim extremists. Other experts, including the journal Science, disputed the diagnosis. Dr. Kean, who had flown to Mexico to examine the Shah, later denied saying the Shah was near death and sued the magazine for libel. In a settlement, the journal said he had acted professionally and ethically. Dr. Kean helped identify the symptoms of turista, or traveler's diarrhea. He and Dr. Sherwood Gorbach identified the E. coli bacteria as the culprit.