BOSTON — The state's unemployment rate dropped a tenth of percentage point to 3 percent in February, as preliminary job estimates from the Bureau of Labor Statistics show Massachusetts added 6,600 jobs last month, according to figures released Friday by the state Executive Office of Labor and Workforce Development. The national unemployment rate is 3.8 percent.The private sector added 5,600 jobs with gains in education and health services; professional, scientific, and business services; leisure and hospitality; trade, transportation, and utilities; financial activities; and construction. Manufacturing lost jobs.The state will release February unemployment rates for local areas, including Berkshire County, on Tuesday.