Southern California air quality officials have proposed a controversial plan to gradually replace the 62,000 cars and trucks in government-owned fleets with state-of-the-art vehicles powered by electricity, natural gas, or other clean-burning fuels. The proposal by the South Coast Air Quality Management District, the first of its kind in the nation, would affect everything from school buses to garbage trucks, as well as privately owned fleets that do business at airports. If adopted by the district board in April, it would require all governmental agencies — from federal to local — to buy clean vehicles whenever they add or replace vehicles. The proposal is causing more of an uproar than any other AQMD rule in recent years. In other California vehicle news, real estate agents are reporting new demand for houses that have four-car garages, some of which, at 1,000 or more square feet, are larger than the typical apartment.