At the request of the Maryland Department of Transportation, Consolidated Rail Corporation recently asked the Interstate Commerce Commission and the Maryland Public Service Commission for an average 20 percent increase in commuter fares between Baltimore and Washington, effective Sept. 30.

Under the proposed increase, the cost of a one-way fare between Baltimore and Washington, now $3, would be increased to $3.60, and the weekly fare, now $15.25, would rise to $18.25.

In a letter to Conrail, Hermann K. Intemann, secretary of the state agency, said the fare increase is necessary to partially recover increased costs the state will incur in providing the service between Oct. 1 and June 30. The cost increase include the additional operating expense of new electric cars recently leased by the transportation department and escalating operating losses.

No fare changes have been made on the route since February 1975. Since then, Conrail reports, costs of providing the service have risen approximately 28 percent.

Trains now run on Mondays through Fridays leaving Baltimore at 6:20 a.m. and 7 a.m. for Washington, and returning from Washington at 5:25 p.m. and 6:05 p.m. Intermediate stations are Edmondson Avenue, Frederick Road, Halethorpe, Odenton, Jericho Park, Bowie, Seabrook, Lanham and Landover. About 1,300 passengers are transported daily.