Pennsylvania Avenue -- the address of every president except George Washington -- should be closed to cars and people in front of the White House, Secret Service officials said yesterday after shots were fired at the executive mansion from the sidewalk.

Closing Pennsylvania between 17th and 15th streets NW is necessary, officials said, as "enhanced security" to protect the president and his family. In addition to creating some traffic problems in downtown Washington, such a move would be further evidence of the extraordinary changes that have been made to protect the occupants of the oldest public building in Washington.

Thick, 38-inch-high concrete posts linked by a chain serve as a protective barrier along the sidewalk in front of the White House. The grounds are surrounded by 10-foot-high fences, and monitors detect any breach on foot or by vehicle. The windows are bulletproof. Antimissile systems reportedly are in place, and the airspace around the White House is restricted to presidential helicopters. Access to the grounds is limited, and tourists must pass through detectors.

Still, breaches occur. Last month, a Maryland man flying a small plane was killed when he crashed on the South Lawn just beneath President Clinton's private quarters. In 1974, an Army private stole a helicopter from Fort Meade and landed on the lawn.

Richard Griffin, assistant Secret Service director for protective operations, said yesterday that closing Pennsylvania Avenue had been requested before yesterday's incident.

But the shots fired from the sidewalk serve to underscore the agency's desire to close the street, he said.

White House Chief of Staff Leon E. Panetta said the agency's recommendation to close the street would be part of a security review of the incident, which will be combined with the probe of last month's plane crash on the South Lawn.

After the crash, Clinton said the White House was "the people's house," and Panetta last night said that there is "a fine balance" between providing security for the president and allowing access to the mansion.

A fence first was put up in front of the White House in 1818.