Sections of Seventh Street NW near Mount Vernon Square have been closed to traffic for two years because of construction work on planned extensions of the Metro subway system's Yellow and Green lines. Metro and city officials say traffic disruptions will continue there for several more years.

D.C. traffic officials say Seventh Street NW had previously been used by about 10,000 vehicles a day. Commuters who had used Seventh Street NW switched to Sixth Street NW and Ninth Street NW. The detour resulted in rush-hour delays of two minutes or less, officials said.

Officials said a section of Seventh Street NW between L Street and New York Avenue is expected to be repaired and reopened by next summer. This move will eliminate a detour and ease congestion for westbound Massachusetts Avenue traffic, which has had to turn onto Sixth Street instead of Seventh Street to bypass Mount Vernon Square.

The first of several recent Metro construction projects affecting Seventh Street NW began in 1983 and is now nearing completion. This $25.8 million project entails excavation of two parallel 1,770-foot tunnels to connect the Gallery Place station with the planned Mount Vernon Square-UDC station. The contract was awarded to Mergentime Corp. and Loram Construction Inc.

The Mount Vernon Square-UDC station is expected to be the northern terminus of the Yellow Line and a stop on the still-unopened Green Line. Those tunnels have been completed, Metro officials say, and other work on the project is expected to be finished by next fall.

Two other projects are expected to cause continuing disruption of Seventh Street NW traffic for several years, officials said. They are a $46.5 million contract to build the Mount Vernon Square-UDC station, which has resulted in closing Seventh Street between M and Q streets, and a $50.9 million contract to build a Shaw station, which is considered likely to lead to closing of Seventh Street between Q and S streets, and possibly as far north as U Street. These stations are scheduled to open in 1990.