AS THE TRACKS of the subway fall into place around the region, will each local government drift into a we've-got-ours-who-needs-yours attitude about service in the other jurisdictions?

Residents and officials have worried for more than a dozen years about the building of a Green Line, running from Southern Prince George's County through Anacostia, Shaw, Cardozo and on out to Greenbelt. For many reasons, it is last on the current construction list -- and there is always concern that it may never be built. It won't be, either, unless residents and governments in Prince George's and the District decide once and for all exactly where the line should or shouldn't go.

Disagreement on this score -- more than the fact that this line would serve many of the poorer sections of the area -- accounts for the low priority of the Green Line. No doubt there was some feeling among the planners years ago that the best way to build support for the subway was to build service first for the affluent and more influential riders; but neighborhood politics -- make that read long and heated disputes -- have held up the Green Line as much as anything over the years.

The line wasn't even a part of the original Mass Transportation Survey or the early recommendations of subway planners -- which gave other lines a good five-year jump in the first place. Today, Mayor Barry still hasn't produced clear administration recommendations for the line in the District. In Prince George's, the routing of the southern leg of the line is still not decided, and there is much litigation still to come once a route is designated. The county government has begun to take up its lists of questions, but progress is slow.

Just because the Green Line may be last on the list is no excuse for dawdling over the decisions that must be made before anything can happen. The governments in the county and in the city should get down to business all the more quickly to keep the Green Line moving along the planning and construction tracks. In turn, the other local partners in Metro should be held to their parts of the bargain -- now and when the time finally comes to go for the Green.