WASHINGTON, Feb 24 (Reuters) - A consumer group sued the federal government on Thursday, saying that salt is killing tens of thousands of Americans and that regulators have done too little to control salt in food. Despite advisories to take it easy on sodium, Americans are now consuming about 4,000 milligrams a day -- nearly double the recommended limit to keep blood pressure under control, the Center for Science in the Public Interest said. So the CSPI renewed a lawsuit first filed in 1983 to ask federal courts to force the Food and Drug Administration to declare sodium a food...