Legislators spend vast amounts of time and money protecting their seats on the Hill. It may surprise them to know that the safest seats in town are probably beneath them.

Since returning from the August recess, members of the House have been protected by new and improved bulletproof seat backs on the floor. The old metal plates that were embedded in the seats have been replaced by a new material designed to prevent the seats from shattering and to reduce shrapnel in an explosion, according to a Capitol official.

The history of the bulletproof seats is sketchy. A curator with the Architect of the Capitol's office said she believes the old metal plates that once shielded representatives from assailants' bullets were installed in response to a 1954 attack by three Puerto Rican nationalists. Sitting in the visitors gallery, the assailants opened fire on the floor of the House, wounding five members.

Other sources indicate the plates were installed after a 1983 bombing near the office of Sen. Robert C. Byrd (D-W.Va.). No one was injured in the incident.

"All I can say is that they are part of an overall, ongoing security enhancement," said U.S. Capitol Police spokesman Lt. Dan Nichols. Because it is a security measure, Nichols said he could not comment further, though he did indicate that House Sergeant at Arms Bill Livingood requested the seat backs, and the project was carried out by the Architect of the Capitol.

John Feehery, press secretary for House Speaker J. Dennis Hastert (R-Ill.), said the speaker approved the installation.

A spokeswoman for the office of the Architect of the Capitol refused to discuss the details of the project, citing security concerns.

The House Sergeant at Arms' spokesman said the seat backs are part of continuing security upgrades.

Officials at the Senate Sergeant at Arms' office said they did not think the Senate had bulletproof seat backs, though they could neither confirm nor deny their existence because of security.

After last July's shootings on the Hill, U.S. Capitol Police started stepping up security at the Capitol. In addition to the $100 million allotted for a visitors center, Congress appropriated $106 million for security enhancements around the building.

The plans were set in motion after a lone gunman, Russell E. Weston Jr., opened fire in the halls of the Capitol, leaving two Capitol police officers dead and one tourist wounded.