The White House on Wednesday issued new rules requiring health insurance companies to provide free coverage for dozens of screenings, laboratory tests and other types of preventive care. The new requirements promise significant benefits for consumers — if they take advantage of the services that should now be more readily available and affordable. In general, the government said, Americans use preventive services at about half the rate recommended by doctors and public health experts. The rules will eliminate co-payments, deductibles and other charges for blood pressure, diabetes and cholesterol tests; many cancer screenings; routine vaccinations; prenatal care; and regular wellness visits for infants and children. Other services that must be offered at no charge include counseling to help people stop smoking; screening and counseling for obesity; and tests for infection with the virus that causes AIDS.