More than 11 miles of new priority bus lanes will be established in the District in July in an effort to speed up rush-hour travel for many bus commuters. However, the new lanes also may slow up some car commuting along a number of major routes into the nation's capital.

Almost 5 1/2 miles of the new bus lanes will be placed along both sides of Wisconsin Avenue NW - between Western Avenue and Calvert Street - where buses now must compete with more than 32,000 cars a day, most of them coming and going during rush hour. Under the D.C. department of transportation plan, the six-lane avenue will have only two instead of three lanes of automobile traffice inbound in the morning and outbound at night.

The other major bus lane additions will include almost 2 miles along upper 16th Street, NW, about 2 1/2 miles on Pennsylvania Avenue SE, in Anacostia, and a short eastbound bus lane on M Street in Georgetown to parallel M Street's present westbound bus lane.

The new priority bus lanes outside the downtown business district, which will cost about $2 million for signs, signals and some construction, were proposed last year but generally ignored in the hullabaloo over other controversial bus lane proposals for downtown Washington, which D.C. officials have now abandoned.

The downtown plan called for making 15th Street one way south as it passes across the Mall by the Washington Monument and making much of downtown 14th Street one way north. The plan was opposed by the National Park Service, among many groups, and city officials are now working on a new downtown traffic plan that is expected to make few changes in present traffic patterns on 14th and 15th Streets. The city and suburban priority bus lanes are designed to improve Washington's mass transit system and reduce reliance on commuting by car, the major source of the area's increasing air pollution.

In a major study of Washington's existing 27 miles of priority bus lanes last spring, D.C. transportation officials found that bus travel was actually slower than automobile travel during rush hours along most routes, even those routes with priority bus lanes. Along M Street in Georgetown in the morning, for instance, the study found buses were averaging only 8.5 miles an hour, compared with an average 13.6 mph for cars. On Wisconsin Avenue local buses presently average 12 mph in evening rush hours, and express buses to Maryland's suburbs 19 mph, compared to 21 mph for cars.

The study estimated that the traveling times of local buses will be increased about 14 per cent and express bus speeds by 24 per cent with the additional bus lanes.

The study blamed lack of police enforcement of the bus lanes for much of the delays caused by illegally parked cars and large numbers of car commuters driving illegally in the bus lanes.

District police officials readily admit that enforceing bus lane regulations has been a low-priority item.

Earlier this month, Mayor Walter E. Wahsington proposed an aggressive parking and traffic enforcement campaign that would more than double the number of parking tickets now being issued. The purchase of 25 new tow trucks to haul off illegally parked cars and the recruitment of a civilian traffic squad to relieve city police officers of much of the routine parking ticket business also were proposed.

In addition to the new M Street and Wisconsin Avenue bus lanes, the city plans to put new priority bus lanes on:

Georgia Avenue NW, on the west side of the avenue near the District-Montgomery County line. The bus lane would be .07 miles long. A .05 mile long bus lanes already exists on the east side of the avenue.

16th Street NW, between U Street and Park Road, 1.8 miles of bus lanes on both sides of the street, to extend the existing 2 miles of bus lanes that extend from U Street downtown.

New York Avenue NE, .05 miles of bus lane just east of Bladensburg Road, to aid Metrobuses coming from nearby storage yards.

Bladensburg Road NE, .05 miles be Bladensburg Road NE, .05 miles between New York Avenue and 26th St, again to assist buses coming from storage yards.

Pennsylvania Avenue SE, adding 2.5 miles, from the Anacostia River to Branch Avenue, to the existing 3 miles of bus lanes along the avenue from the Capitol to the Anacostia River.

South Capitol Street, .27 miles by building a third southbound lane at intersections with Martin Luther King Avenue.

13 Street SE, .19 miles, from W Street to Good Hope Road.