War abroad could hit home in the nation’s chemical factories and food-processing plants, the General Accounting Office warned yesterday. The GAO said the lack of federal authority over such facilities makes it impossible to know whether they are sufficiently prepared for potential terrorist attacks. The office recommended that the U.S. EPA and the Department of Homeland Security take joint responsibility for ensuring the safety of chemical plants, while the departments of Health and Human Services and Agriculture oversee food-processing plants. Since Sept. 11, 2001, agricultural experts and others have been haunted by the possibility of intentional contamination of the nation’s food supply, for example with bacteria such as salmonella or E. coli. The nation’s 15,000 chemical and petroleum plants, many of them located near populated areas, are also a worrisome weakness. In response to the report, Homeland Security Secretary Tom Ridge asked the Coast Guard step up patrols near some important chemical facilities, and some state agriculture officials have begun warning farmers to keep a careful watch over their fields.