Families of American government officials in northern Thailand have been evacuated because of possible violence from drug traffickers, a U.S. Embassy spokesman in Bangkok said. "We recently received reports of a potential narcotics-related threat to U.S. government personnel at our consulate in Chiang Mai. We took this seriously," spokesman Ross Petzing said. An undisclosed number of American dependents began leaving Chiang Mai, about 430 miles north of Bangkok, for the capital last Monday, he said. Thai police said the threat may be related to an Oct. 20 raid that netted about 1,500 pounds of heroin--the biggest heroin seizure in the country's history.