When all is paid and done, will Greater Washington's subway system serve the region -- and connect with bus lines -- in an efficient and useful transportation network? Or will the rail system wind up shortchanged, curtailed and ill-served by a series of fragmented local bus systems run by different jurisdictions? Right now Congress is making an important decision about the subway -- while various suburban

governments are breaking away from the regional Metrobus system and starting their own lines. All of these decisions -- though being made by different governments -- are related to each other. But the immediate danger is on Capitol Hill, where a decision to reduce subway financing too sharply could jeopardize the whole regional transportation system.

There is an important difference between what the House has approved for Metro construction and what the Senate Appropriations Committee did to the subway-money request. In dollars, the difference is between a 25 percent cut in the Senate and a five percent cut in the House. Transit officials have noted that the House cut would be workable; but a 25 percent reduction could ruin the long- agreed-to plan to expand the rail system to 89.5 miles by the early 1990s. This plan includes a Green Line extention to Greenbelt and a Yellow Line spur to Alexandria's West End.

Metro and the Reagan administration had initially sought $250 million but still could manage with the House figure of $237.5 million. Anything less would not only threaten the entire subway network as envisioned for decades but also upset efforts to coordinate with bus service. Local governments already are taking on a number of risks by starting their own bus lines -- with long-range financing implications still anything but clear to the taxpayers. Without some semblance of stability in subway construction, the mapping of convenient bus service -- and the costs of it -- would be left in limbo.

The Reagan administration has recognized the importance of orderly subway construction and has been closely monitoring the progress. The idea has been to spread available money as evenly as possible. That makes "cost-efficient" sense -- and if conferees can see this as well, they will work to appropriate the $237.5 million that would allow progress to proceed.