The map tells the story. An auto-free, tree-covered greenway for cyclists and walkers should soon stretch from the National Mall to Baltimore's Inner Harbor.

The greenway's core is an area of about 40 square miles of never-to-be-developed land that includes Fort Meade, most of which will be a national park; the Patuxent Wildlife Research Center; the USDA National Agricultural Research Station; and Greenbelt National Park.

At its southwestern end, the greenway's core will be connected to the District by Prince George's Northeast Branch and Northwest Branch Stream Valley parks.

Within the District, the greenway will use National Park Service land connecting Civil War forts, then turn south at Fort Totten through Catholic University on the route of the proposed Metropolitan Branch Trail. From Brookland almost to Union Station, the Met Branch will use former siding land, about 100 feet wide, that will become a linear park. At the urging of the Rails To Trails Conservancy and with the support of numerous county and city officials and U.S. Sens. Barbara Mikulski (D-Md.) and Brock Adams (D-Wash.), the D.C. budget now includes $1.5 million in capital authority to acquire the former siding land.

At its northeastern end, the Fort Meade/Patuxent/Research Station greenway core will be connected to Baltimore in two segments. It will get as far north as Baltimore-Washington International Airport primarily using WB&A road, a lightly traveled road built on the former Washington, Baltimore and Annapolis tracks. Under plans now being developed by the Maryland Department of Transportation, the trail will go from BWI to downtown Baltimore along the Baltimore Light Rail line.

Many pieces of a Baltimore- Washington greenway have been on the map for a long time, put there by the efforts of many people over many years. From their efforts, and the efforts of getting a few last pieces in place, the greenway is becoming a reality. Perhaps no other two cities on the East Coast, or even in the country, will be able to boast of being connected by a greenway comparable to the one now emerging between Baltimore and Washington.

-- Patrick H. Hare -- Betty Ann Kane are, respectively, general coordinator of the Coalition for the Met Branch Trail and executive director of the coalition. Our household was glad to see the Nov. 16 editorial "Bring Back the Anacostia." During the past few years, we have been pleased that more efforts have been focused on this important task. We visit the Northwest Branch in West Hyattsville and the Anacostia River near Bladensburg regularly for walks, bike rides and nature exploring with our three boys. We have also been involved in restoration efforts -- litter cleanups, tree planting and labeling storm drains "Chesapeake Bay Drainage -- Do Not Litter." We agree with The Post that grass-roots involvement and sustained public funding are essential if we are to restore the Anacostia.

The Post's final editorial thought, though, is the key to further progress: "Citizens can actually help -- if they'd only learn to look at this underappreciated and all-but-invisible waterway."

Just such an effort is underway that will make it easier to see the Anacostia. Citizens and municipalities in northern Prince George's County are banding together to create the Anacostia Headwaters Greenway. Central in this effort is getting federal-aid highway funds for completion of the long-planned 24-mile bicycle and pedestrian trail network along the Anacostia tributaries of Sligo Creek, Northwest Branch, Northeast Branch, Indian Creek and Paint Branch. Completing the streamside trails is probably the simplest and cheapest way (13 miles are already in place) to make these invisible waterways visible again and central in residents' relationship to their surrounding environment.

Even more exciting is that these trails will create seven direct-access links to new Metro Green Line stations at College Park and West Hyattsville. People will be able to abandon the congestion and hassle of auto commuting for an efficient bike-and-ride transportation system. Replacing auto trips with nonpolluting transportation also is critical for the ultimate cleanup of the Anacostia.

Prince George's citizens should support the county council and Paris Glendenning in their request for federal highway dollars, funneled through the State of Maryland, to fund completion of these hiker-biker trails. Urban trails are one way to get polluting auto users (and that includes most of us) to clean up their own mess. Urban trails also help us teach our children to care for their environment and provide an outlet for fun and exercise for city dwellers.

-- Robert S. Patten