The Energy Department's Energy Information Agency said gasoline prices this summer will fall as much as 28 cents a gallon below levels recorded last summer. It predicted that this summer's prices for all grades of gasoline would average between 80 cents and $1.05 per gallon, compared to $1.22 in the summer of 1985. In its quarterly projections, the agency also forecast that motorists would drive about 5% more this summer than they did a year ago, due largely to lower gasoline prices and higher personal incomes. In its long-term forecast, the agency said gasoline prices would begin rising late this year and continue to climb into 1987 because of the expected increase in world oil demand. According to the report, gasoline prices are likely to remain below their 1985 levels through mid-1987.