IN A MOST significant vote, Virginia's Senate has approved a sound tax plan to help finance Metro as well as other transportation needs. The measure, introduced by Sen. Omer L. Hirst (D-Fairfax), would allow a 1-percentage-point increase in the sales tax in Northern Virginia to help finance Metro's operating costs and to pay for certain highway and parking improvements. Under the bill, which now goes to the House of Delegates, two-thirds of the revenue would go toward Metro expenses and the other third for such things as special highway lanes for buses and car pools, and for parking lots.

The measure would be subject to approval by elected representatives of 90 percent of the estimated 850,000 people who live in the Northern Virginia transportation district. That's not only a ratification provision; it means that if the tax were disapproved in, say, Fairfax City, it could be assessed on the entire region anyway. (As you may recall, Fairfax City was able to hurl a monkey wrench in the form of a veto of a local gasoline-tax proposal last year).

The question now is whether House members will recognize the merits of the Senate approved plan - which, among other things, would ease some of the property-tax burden now felt by homeowners.These pressures are shared by taxpayers all over the state - voters who will be looking more and more to their representatives for practical, regional approaches to financial planning in the state. They are seeking relief from property-tax bills, which would be affected under this sort of sensible formula. As Sen. Hirst noted, "The purpose is to regionalize both the levy and the benefits . . . Part of the bill requires us to come up with a regional transportation plan."

Another sponsor of the bill, Sen. Wiley F. Mitchell (R-Alexandria) - hardly considered a free-wheeling spender - noted that the measure not only would eliminate a substantial burden on the property tax, but would "distribute the burden of Metro costs over a broader segment of the population" and would also eliminate "the constant bickering over how future deficits might have an impact on different jurisdictions."

Those are certainly appealing propositions. We believe voters can see the sense in this approach - and now it's up to members of the House to demonstrate their sensitivity to property-tax problems as well as transportation needs of Virginians, with a solid vote of support for the Senate measure.