WASHINGTON (AP) _ That mail truck rolling through the neighborhood may soon be burning natural gas instead of gasoline.

The U.S. Postal Service awarded contracts to two companies Wednesday to covert 1,463 of its local mail trucks to run on compressed natural gas.

The agency already has about 1,000 trucks that burn natural gas, which produces less exhaust emissions and requires less engine maintenance than gasoline-powered vehicles, officials said.

For equivalent mileage the natural gas costs about 72 cents a gallon compared to between 97 cents and $1.09 for gasoline, postal officials said.

Both natural gas and gasoline are fossil fuels, but while gasoline must be refined from various grades of oil, natural gas comes from the ground in gas form. Natural gas, widely used for cooking and home heating, is compressed for convenience in carrying on the vehicles.

The contracts announced Wednesday are to Mesa Environmental of Fort Worth, Texas, $1.2 million to convert 581 vehicles in the West, and to Beacon Power Systems of Troy, Mich., $2.1 million to convert 882 vehicles in the Eastern and Southern states.

The conversions will be done in Denver, Hartford, Conn.; Newark, N.J.; Martinsburg, W. Va.; Decatur, Ga.; Baltimore, Bethesda and Columbia, Md., Tampa, Sunrise and Davie, Fla. and Chula Vista, Irvine, Corona and Long Beach, Calif.

Postal officials said cities were selected for the conversions primarily because of cooperation with local utility companies, which will supply the natural gas.

After conversion, the vehicles will still be able to burn gasoline if necessary.