The sponsor of a bill to install antiterrorist barriers at two entrances to the U.S. Capitol grounds said yesterday that an incident in which a car raced past a sentry post and sped by the Capitol "points out the need to move ahead with improvements to the security of the East Plaza."

"These are the incidents we have been scared about," said Rep. Robert A. Young (D-Mo.), chairman of the House Public Works and Transportation subcommittee on buildings and grounds. "We're just lucky it wasn't a terrorist."

Early Tuesday, in what authorities described as a traffic incident, a car passed a security post at the New Jersey Avenue SE entrance to the Capitol grounds and entered the East Plaza parking area. The car went by the east front of the Capitol, veered to avoid a barricade on the north side of the plaza and hit a wall, causing it to sail through the air over a car parked on Constitution Avenue. It continued into Senate Park, where it crashed into two trees.

Capitol police said no explosives or weapons were found in the car. The driver, Rodney Parker, 30, of 2403 Southern Blvd., Temple Hills, who was charged with driving under the influence of alcohol, speeding and reckless driving, was in fair condition yesterday at Washington Hospital Center with head injuries and multiple lacerations on his face, arms and hands, a hospital spokeswoman said.

A police car, often with its engine running, is positioned near the New Jersey Avenue entrance to block any vehicle trying to pass the checkpoint without permission, but U.S. Capitol Police spokesman Bob Howe said yesterday that the officer in the car did not have time to react.

"I wouldn't call it a lapse" in security that allowed Parker's car into the grounds, Howe said. "The system we have out there now is better than no system at all, but it's by no means perfect . . . . There's no way to improve upon it with what we have. Congressman Young's bill would alleviate that problem."

Part of the proposed legislation calls for the installation of curved steel plates that can be raised and lowered electronically at the New Jersey Avenue SE and Delaware Avenue NE entrances to allow vehicles to pass. Those entrances are the only ones to the Capitol that have not been blocked with concrete barriers or large trucks.

Young's bill, which carries a price tag of about $8.4 million, also proposes to convert much of the east plaza of the Capitol into a park by tearing up the asphalt and replacing it with imported sheets of granite. Two water fountains would be added and the two temporary wooden guard posts at the street entrances would be replaced with permanent ones.