GOV. HARRY R. HUGHES has offered an extra, one-time-only grant to help pay the Maryland suburbs' share of Metro's projected operating losses this year. Legislators from Montgomery and Prince George's counties are umderstandably disappointed by the proposal. They have been seeking complete state assiatance to meet their local financial obligations to the rail and bus system, through a portion of the state's sales-tax revenues. Given increasing federal pressures on all Metro jurisdictions to agree on some kind of tax formula to pay for Metro, the effort to commit some of the sales-tax revenues deserves the governor's support.

At least Gov. Hughes is sympathetic to the financial problems of Metro as well as the reponsibility of the state to assist. That puts him well ahead of Virginia Gov. John N. Dalton, whose narrow preoccupation with "uniform" taxes throughout the state helped kill a sensible tax plan sought by Northern Virginia residents and lawmakers. Actually, Gov. Hughes's plan would yield almost the same amount for Metro as a 1/4-cent-of-sales-tax-revenues formula -- but only for one year. Under the governor's proposal, the state would distribute a portion of the tax on sales of new cars to Montgomery and Prince George's counties and to Baltimore. But this does not establish any permanent, reliable financial plan.

Acknowledging this, Gov. Hughes says his measure would provide time to study more complex approaches, including raising the gasoline tax or corporate income tax. If such study between sessions of the legislature were given top priority and a pledge of serious action next year, it may be the best that Metro's supporters can hope for -- since there are enough Republican, rural and Baltimore suburban opponents of the sales rebate to turn the effort into a nasty legislative battle.

There is, for example, this provincial view offered by State Sen. Walter Baker, a Democrat from Cecil County: "Why should my people on the Eastern Shore pay for this project? I can see it coming. It's going to cost us more and grease this state along the track of socialism." Under that logic, perhaps the people in Montgomery and Prince George's counties should insist on getting as much revenue back from the state as they put in -- and not pay for anything in another part of the state.

Gov. Hughes knows better than that, and recognizes the growing reluctance of Congress to help underwrite subway construction unless the governments of this region guarantee that they will cover the transit system's operating deficit. Those legislators in Annapolis who share this understanding should continue to work with -- and on -- the governor to see that his efforts on behalf of Metro do not flag.