ANNAPOLIS, JAN. 17 -- Gov. William Donald Schaefer plans to ask the Maryland General Assembly on Friday to extend the state's 5 percent sales tax to gasoline to help restart road construction programs, according to legislative leaders and gubernatorial aides.

Applying the sales tax would be the equivalent of raising the tax on gasoline, currently 18.5 cents per gallon, by 6 to 7 cents. The levy was raised five cents in 1987. And the new proposal, if approved, would give Maryland the highest motor fuel tax in the region.

The need for new roads and bridges was mentioned prominently in the governor's inaugural speech Wednesday. "If the state won't invest in Maryland, how can we expect businesses to?" he asked.

Aides said they expect the gasoline sales tax to be part of Schaefer's State of the State address to a joint legislative session. But Schaefer can expect strong opposition from Speaker R. Clayton Mitchell Jr. (D-Kent). "There is no gas tax," Mitchell said. "Absolutely not." He argues that voters indicated in November that they oppose new taxes, adding that perhaps the real problem is the size of state government, not insufficient revenue.

In presenting the first legislative package of his second term, the governor also is expected to call for further restrictions on ownership of military-style assault weapons and for holding adults liable if their guns get into the hands of minors. Two years ago, Schaefer led the effort to preserve Maryland's unique law banning the sale of cheap handguns.

He also plans to seek approval for controversial growth controls designed to channel development into urban centers and away from environmentally sensitve areas. It was unclear today how far Schaefer will go in trying to move the state into land-use decisions jealously guarded by local governments.

Before the legislative session began last week, Schaefer aides confirmed that he hoped to expand the vehicle emission inspection program to another five counties and tighten restrictions to meet new federal clean-air requirements.

For nearly a year, the Schaefer administration has been dropping hints that it would ask for an increase in gasoline taxes in 1991 to replenish the transportation fund. The sour economy, coupled with lower gasoline consumption and the expediting of some projects, has nearly depleted the treasury used to finance roads, bridges and mass transit construction programs.

Citing the possibility of a looming deficit, Schaefer last month halted all new construction projects. And Department of Transportation officials said today that those projects will be on hold for 18 months unless additional taxes are approved. Today, officials also forecast long delays or cancellation of plans for projects such as the Eastern Bypass through Prince George's County, the Bethesda-Silver Spring trolley and the connector between Interstate 270 in Montgomery County and Interstate 95.

Transportation Secretary James Lighthizer said he urged Schaefer to seek a five-year, $1.5 billion state transportation construction program.

Lighthizer said he favors the sales tax route because it would be "inflation-sensitive," rising along with the price of gasoline.

But a Schaefer aide said later he expects the governor to propose a $1.3 billion package that would call for the sales tax and sharply higher truck and Motor Vehicle Administration fees.

At a meeting of the House Appropriations Committee today, legislators grilled transportation officials about projected shortfalls in their budgets, many expressing anger that projects promised in 1987 may not be completed.

They also questioned Schaefer's proposal to take up to $100 million from the transportation fund to help fill a gap elsewhere in the budget for the year beginning July 1.

"That's ludicrous . . . when you're asking us for a revenue enhancement," Del. John G. Gary (R-Anne Arundel) said.