Washington — Fourth of July weekend motorists will find gasoline plentiful and prices lower, the American Automobile Association says. The national average price of gas dropped in June for the second straight month, to $1.374 a gallon, down 1.1 cents from May and 2.1 cents from April. But prices still averaged more than 12 cents a gallon higher than a year ago. The highest prices in the continental United States were reported in Mississippi, where the average was $1.451. The lowest average prices were in Ohio -- $1.307.