East Executive Avenue, the thoroughfare flanking the White House that is a popular shortcut for thousands of commuters, will be closed until at least September and may be closed permanently, according to National Park Service officials.

The avenue, which handles more than 10,000 cars daily, was closed March 17 because of construction of a new $771,000 security screening pavilion for White House visitors.

But the park service has decided to extend the closure as a "tourist season tryout" with an eye toward possibly eliminating the road, redesigning and landscaping the area, said National Park Service spokesman Sandra Alley.

Safety of the 7,000 to 10,000 daily visitors to the White House was the main reason for the decision, Alley said. The park service, which controls the federally owned roadway, said there were 17 accidents last year on East Executive.

The avenue, running between Pennsylvania Avenue and E Street NW and separating the White House and the Treasury Building, is one of the main north-south routes for downtown Washington and its closing has resulted in heavier traffic on 14th, 15th and 17th Streets NW. City transportation officials said, however, that the increase has not been dramatic since the closing last month.

"We have sympathy with those who might have problems commuting, but we have to think of our responsibility to the 10,000 persons who go there just about every day," Alley said.

"It was never designed as a commuter shortcut," she said. "People discovered it, and it is convenient, but what we have to look at is taking care of the visitors."

The decision to extend the closing was made by Manus J. Fish, director of the National Capitol region of the U.S. Park Service.

Thomas Downs, the D.C. director of transportation and public works, said the department will begin studying the resulting changes in traffic flow, and will adjust the traffic signals near the White House to ease possible rush-hour bottlenecks.

Meanwhile, D.C. transportation officials said southbound commuters who have used East Executive should now use 14th or 15th Streets, while northbound drivers can use 14th, 15th, 17th, 18th or 20th streets.

The White House has favored closing the avenue to safeguard visitors for more than 20 years, according to Rex Scouten, the White House chief usher who has overseen the building and grounds since 1949.

"Why we have not had more people hurt badly there, I think it is a miracle," Scouten said. Visiting families and children congregate on the sidewalk awaiting White House tours, and frequently spill over into the street, officials said.

The park service will consider this fall whether to close East Executive permanently, depending on how the temporary closing affects both pedestrian and vehicular traffic around the White House. The public entrance at the east lawn of the White House is being remodeled to include a new entranceway equipped with a magnetometer and other devices to check visitors for guns, bombs, knives, munitions and other items. Among various plans, the park service is considering rebuilding the street with paving stones, and adding park benches and landscaping, officials said.

Downs called the park service plan "obviously reasonable" and said he did not believe the closing would cause major problems. He said park service officials discussed plans last fall to close the street temporarily, but have not yet informed the D.C. department of their current plan. "It is their street. We are the nation's capital and if they need to have it closed for security reasons . . . . We are not going to oppose it," Downs said.

In the original design of the White House grounds in 1791, the land surrounding the White House was to be part of a "President's Park" and East Executive Avenue did not exist. The avenue was cut through the grounds during the administration of Ulysses S. Grant in the 1870s to accommodate the public for visits to the White House. The avenue was closed for security reasons during World War II, and is also closed several times a year for special events such as the annual Easter egg roll.

West Executive Avenue, which runs between the White House and the Old Executive Office Building, was closed permanently in 1951 after the assassination attempt against President Truman.