Each year at this time, both the diversity and sophistication of Greater Washington's many governments are put to test as the elected officials from around the region, the states and the federal government gather for Metro's year-end hat-and-buck-passing policy review. And though these sessions rarely begin with total harmony, they have been marked over the years by notable interjurisdictional agreements that have overcome seemingly impossible political and financial obstacles produce a working, growing subway system. This week's conference, which opens today,

will be no exception; financing continues to challenge the fiscal ingenuity and cooperative spirit of the governments as they pore over route maps and budget estimates. Certain results are critical:

It's got to be the Year of the Green Line. That means agreeing on a complete route through the District and Prince George's County, as well as the financing arrangements. Resolution now is essential, to clear the last court hurdles and start making visible things happen.

Metro's budget should reflect the frugality that general manager Carmen Turner and this year's Metro board president, John Milliken of Arlington, have been emphasizing. Tight constraints on personnel, spending policies and transit fares can and should be strong arguments for appropriate and necessary federal support of the construction schedule that Metro's board and all its local member governments have agreed to.

Commitment to the entire 101-mile subway system has to remain, and the understanding of the administration and Congress is essential if everyone is serious about a reliable construction timetable that could save ig money and bring service to those who have paid and still wait at the unfinished ends of the lines.

There's the matter of buses, too -- buses that don't come often enough, that don't exist or that should be operated by somebody other than Metro. This is not something that can be hammered out in two days of meetings. But neither can it proceed if the representatives get into endless arguments over cost and mileage formulas that have never been perfect, anyway. The bus system -- whoever runs what -- has got to be integrated with the subway system, or mass transit won't be doing what it should be after all is said and built.