For thousands of Virginia commuters who encounter time-consuming traffic snarls driving into Washington, the good news is that work on reconstructing the approach to the 14th Street bridge is right on schedule.

The bad news is that the schedule does not call for completion of the work until almost 16 months from now -- on Aug. 1, 1982.

Meantime, three of the former six lanes on 14th Street between Independence Avenue and the bridges have been closed to traffic. The three open lanes are being used only for northbound traffic headed toward downtown Washington during the morning rush, but are subject to closure at other times. Virginia-bound traffic has been shifted to 15th Street.

The 14th Street reconstruction is a major project costing $13 million. But that is not evident to many of the 40,000 drivers who use the street on an average weekday. A concrete barrier higher than the eye level of most drivers hides the work from view.

So far, according to Bernard J. O'Donnell, deputy director of the D.C. Department of Transportation, the work has consisted mainly of removing old pavement, dismantling the trestle-like structure and salvaging as much of the existing steel as possible.

When the project is completed, the roadway will have three 12-foot-wide lanes in each direction, plus shoulders and a high median barrier. The old roadway had 10-foot lanes and a low median.

Federal funds are paying for 90 percent of the project's cost.

The affected section of 14th Street was built after World War II at a time when the Potomac River highway crossing was a single old-fashioned truss-topped bridge. It has been replaced by three modern, parallel bridges. Most of the cross-river traffic -- about 100,000 vehicles a day -- now gets to and from Washington via the Southwest Freeway (Interstate Rte. 395). City traffic officials have urged this as the primary detour around the construction zone.

Although motorists using 14th Street tell of frequent rear-end or fender-bender accidents. O'Donnell said only one official accident report has been filed in the construction zone since work on the project began last August.