Virginia Gov. Gerald L. Baliles, in an unannounced move, today endorsed an increase in the state's gasoline tax that would raise the cost of gasoline by a cent a gallon to generate revenue to plan for highway construction.

Baliles' proposal was offered in the House Finance Committee by Del. Warren G. Stambaugh (D-Arlington) while the governor's aides stood in the back of the committee room.

The measure also would retain a subsidy for producers of gasohol, an engine fuel that consists of unleaded gasoline and alcohol.

The proposal calls for setting the gasoline tax at 15 cents a gallon, 4 cents more than the current rate. But 3 cents of the increase would come from converting the state's 3 percent excise tax on gasoline companies to a direct 3-cent-a-gallon tax on gasoline. The companies have been passing on the excise tax to consumers and would be expected to stop that practice if the excise tax were stopped.

Baliles' proposal would raise about $50 million during the next year for planning of massive highway construction that is expected to be recommended in September by the governor's transportation commission.

The proposal today was the first public indication of how Baliles wanted to raise money for future projects while the commission studies the issue.

Baliles previously had endorsed the idea of more money but had refused to support specific proposals in a bill by Sen. Edward E. Willey (D-Richmond) to raise about $200 million a year in highway construction funds by increasing the gasoline tax 1 cent a gallon, abolishing the gasohol subsidy and raising fees for vehicle registration.

Stambaugh introduced the administration's proposal during a long committee meeting in which the House made it clear it was unlikely to go along with the proposal by Willey, chairman of the Senate Finance Committee. Willey's measure already has passed the Senate.