Police patrol the Capitol armed with rifles and wearing biological, chemical and radioactive attack gear. One senator was so concerned about the terrorist threat that he temporarily shut down his office during the recent pre-election recess.

But more than three years after Sept. 11 (search), Congress has yet to decide how it would respond to a catastrophic event that kills or incapacitates many or most of its members.

"The Capitol building has to be one of the prime targets in the world," said Rep. Brian Baird (search), D-Wash., a crusader for better congressional preparedness. "But we have yet to make true provisions either for congressional continuity or presidential succession."

"It's an immense disappointment to me," said Norm Ornstein, a scholar at theAmerican Enterprise Institute (search) and senior counselor to the Continuity of Government Commission, a nonpartisan group formed in 2002 to study how to keep Congress functioning after a disaster.

The commission, led by former Sen. Alan Simpson, R-Wyo., and former Clinton White House counsel Lloyd Cutler, concluded that Congress must amend the Constitution to ensure its survivability in an age of terror.

The problem is more with the House. The 17th Amendment, ratified in 1913, allows governors to temporarily appoint replacements to empty Senate seats until special elections can be held. But the Constitution requires that House vacancies be filled by direct election.

That, many warn, could lead to a lengthy legislative void if a majority of members are killed or incapacitated in an attack and it takes months to stage elections to replace them. It's commonly believed that Congress narrowly escaped that fate on Sept. 11, 2001, when passengers on United Flight 93 resisted their hijackers and the plane, possibly heading for the Capitol, crashed in Pennsylvania.

Security concerns have only grown since then. Security will be so tight at President Bush's inauguration in January that people working in the Capitol will need special clearance, and new photo IDs, just to get in the building.

But there's been strong resistance in the House, led by Judiciary Committee Chairman James Sensenbrenner, R-Wis., to any constitutional change allowing for the temporary appointment of members.

The House "is rooted in democratic principles and those principles must be preserved at all costs," Sensenbrenner said in April when the House passed his legislation requiring expedited special elections within 45 days after the speaker of the House confirms that 100 or more members had been killed in an attack.

The House Rules Committee is also working on new rules that would allow the speaker, after crossing several procedural barriers to assure there was no political manipulation, to lower the number of members needed to constitute a quorum.

But critics say the quorum change is unconstitutional and expedited elections would still leave Congress paralyzed for weeks or months at a time of dire national crisis.

Last June Baird offered a constitutional amendment under which governors could appoint representatives, to hold office until special elections can be held, when a majority of the House is unable to carry out its duties because of death or incapacity.

But with the Republican leadership strongly against it and controlling the debate, it was soundly defeated. "Of all the issues to create partisan divisions," Ornstein said. "It's just a mystery."

The Senate has yet to pass Sensenbrenner's bill. Instead, Sen. John Cornyn, R-Texas, in May pushed through the Senate Judiciary panel he heads a constitutional amendment giving states a choice on how to fill House and Senate vacancies, either by appointment or special elections.

Cornyn is also the lead senator on another macabre subject — redefining the line of succession in the event the president and vice president are killed or cannot serve.

Just about everyone agrees that the current law, from 1947, is flawed. It places the speaker of the House and the president pro tempore of the Senate next in line after the vice president, followed by the secretary of State and the heads of other cabinet departments in order of their creation.

Rep. Brad Sherman, D-Calif., sponsor of a presidential succession act in the House, said the will of the people could be subverted if a congressional leader from a different party ascended to the presidency — a scenario that has been depicted in the TV presidential drama "West Wing."

Sherman, at a recent hearing, added that "current law could mislead terrorists into believing that by killing the president and vice president, they could alter U.S. policy."

Sherman, like Cornyn, would remove the speaker and president pro tem from their current spot in the line of succession. Sherman also would add senior ambassadors to assure a successor in the event an attack killed all those living in Washington.

Cornyn said presidential succession legislation may have a better chance of advancing because "in some ways it's less personal to the members of Congress." He said he understood "the natural impulse not to want to contemplate your own demise. But we have a greater responsibility here."