Top Washington area political leaders unanimously agreed today to seek specially dedicated taxes from their legislative bodies to pay the construction costs for the Metro subway and the operating costs of the combined bus and subway system.

The carefully worded resolution permits a different type of "reliable, dedicated source of revenue" from Maryland, Virginia and the District of Columbia in recognition of the political impossibility of a single region-wide tax that could be approved in the three jurisdictions.

The resolution was adopted at the conclusion of a two-day conference on Metro here attended by about 200 people, including elected officials from all area governments and members of both the Maryland and Virginia legislatures.

The resolution has no legal standing but nonetheless represents the first regionwide affirmation of area political leaders that they are still committed to completing Metro after two years of studies and funding delays.

Thirty miles of Metro's planned 100-mile system are operating; another 30 miles are under construction and fully funded. But 40 miles remain and about $3 billion- $551 million of it from local or state sources-will be needed before Metro can be completed, according to the latest cost estimates.

Transportation Secretary Brock Adams has committed the federal government to the "goal of completing the 100-mile system," as he puts it. At the same time, however, he told the area leaders for a second time Friday night that a full-system federal funding commitment will depend on whether the local area governments can solve Metro's continuing financial crises by earmarking and guaranteeing tax revenue. Almost all big-city U.S. transit systems have guaranteed tax sources.

Delegates from both Maryland and Virginia said they will be seeking special funding mechanisms for Metro in their upcoming legislative sessions.

In Maryland, under the idea most frequently discussed by delegates here, 1 percent of Maryland's 5 percent general sales tax would be earmarked for the state's transportation trust fund.

Once in that fund, it could be spent for transit projects in the Baltimore and Washington areas, for roads in Garrett County and for reilroad improvements on the Eastern Shore. That approach would have the advantage of appearing to be something for everybody without actually involving an increase in the tax rate consumers pay.

Such a proposal will be made in the legislative session, delegates said.

In Virginia, the Northern Virginia delegation is going to try once again to get permission from the General Assembly to raise the sales tax in Northern Virginia from 4 percent to 5 percent, and dedicate the additional percentage point to transportation projects.

At the same time, there would be a penny-for-penny decrease in the property tax rates charged Northern Virginia homeowners and business. The effect would be to shift the Metro burden from the property tax to a more generally based sales tax. That same proposal passed the Virginia Senate last year but failed by one vote in the House. Virginians agree that it must not only pass the House, but pass the House convincingly to avoid a veto from Gov. John Dalton, who has said time and again that he opposes state aid to reduce Metro's operating deficits.

The District the Columbia, ironically, has more local autonomy in the maters than its suburban neighbors. A variety of state-like taxes is available to the D.C. government, including sales taxes, income taxes, payroll taxes and a number of other taxes. Some combination of those taxes was discussed by D.C. representatives here, but no firm conclusion was reached.

However, the payroll tax has been most often suggested as the appropriate D.C. vehicle for Metro purposes. D.C. does not want to be the only area jurisdiction with a payroll tax, however, because that would invite employers to locate in the suburbs.

Therefore, the District delegates pushed strongly for inclusion in the resolution language that would commit the Metro board to seeking a "uniform regional funding source." "If that's not in the resolution I will vote against it," said D.C. Transportation Director Douglas N. Schneider.

"This is an issue which will divide us and not unite us," said Prince George's County Councilman Francis B. Francois. "There is no mechanism for enacting a regional tax."

"The term regional tax implies regional taxing authority," said Virginia Del. Elise B. Heinz (D-Arlington/Alexandria). "There is no way in this century we can get that through the legislature."

The carefully worded compromise resulted from that discussion.

There was also moderation in what is threatening to become a major city-suburban split over transit fare levels. Suburban jurisdictions, concerned about rising Metro deficits, have called for fares to increase in relation to the Consumer Price Index.

D.C. opposes that, but Schneider and Council Chairman-elect Arrington Dixon said D.C. is willing to consider a fare adjustment formula based on factors stressing the ability of an individual to pay.