I'm not really sure which path you might mean. There is an unnamed path that goes from Marshall Dr by the Iwo Jima Memorial and alongside Arlington National Cemetary. However, once you cross Memorial Dr it is nothing more than a rut in the grass alongside the Jeff Davis Hwy to Washington Blvd north of the Pentagon. Arlington's bike map also shows a paved spur off the Mt Vernon Trail over to Washington Blvd north of the Pentagon. Both of these are actually directly west across the Potomac from the Jefferson Memorial.

Going south, there is only the Mt Vernon Trail until you get south of the airport when you can connect heading west to the 4 Mile Run Trail (and over to the W&OD trail) and ride almost 50 miles out to Purcellville.