Maryland is proposing a six-year program to improve its truck scales, in response to federal requirements for enforcement of the state's weight limit laws for federal-aid highways.

The Maryland Department of Transportation plans to have five modern truck weighing stations by 1984, instead of the present three, which are obsolete.

The state's proposed program calls for new scale houses on I-83, between the Baltimore Beltway and the Pennsylvia line; renovation of scale houses on U.S. 13 in Salisbury and U.S. 40 in Cecil County, and on the weigh station on U.S. 301 in Upper Marlboro.

The Upper Marlboro weigh station will eventually be replaced by modern facilities on Maryland Rte. 3, and the scale houses on Route 40 in Cecil County will be replaced by new facilities farther south on Route 40 in Baltimore County.

The total cost to update the three existing weigh stations, build four new ones and to staff, operate and maintain them for the next six years would be about $26 million, according to the Maryland Department of Transportation. The money would also increase the number of roving police patrols using portable scales from 11 to 17. Federal aid would cover about one-quarter of the cost.