A biological or chemical attack leaves hundreds of lawmakers too sick to show up at what may be a destroyed Capitol. Others are ready to carry on, but, under rules of Congress, they may be forbidden to act at a time of dire national emergency.

The House and Senate define a quorum (search), the number needed to do business, as a majority of members "chosen, sworn and living." In the House, that means 218 if all 435 seats are filled.

But what happens, asked House Rules Committee Chairman David Dreier, R-Calif., if 225 members are left alive but incapacitated by a catastrophe. The 210 remaining lawmakers, he said, would fail to constitute a quorum.

Dreier's committee met last week to discuss how to prepare for mass incapacitation, part of an ongoing effort in the post-Sept. 11 era to assure that Congress will continue to function after a cataclysmic attack.

Earlier in April, the House passed legislation requiring affected states to hold special elections within 45 days after the House speaker declares that a disaster has left more than 100 seats vacant.

The bill dissatisfied many lawmakers. Some would rather have a constitutional amendment (search) to allow the House, like the Senate, to fill temporarily seats by a governor's appointment so as to avoid lengthy gaps in its ability to pass laws.

The House-approved bill also deals only with vacancies created by death, not incapacitation.

The Continuity of Government Commission (search), a high-level nonpartisan group created in 2002, noted in a report last year that having a few nonfunctioning members is not new to Congress, but "the loss for weeks, months or years of tens or hundreds of incapacitated lawmakers is another story."

As an example, it said, "a chemical attack might leave thousands in burn units or with respiratory and neurological injuries. If such an attack were centered on Congress, many members could be in hospital intensive care units for months."

The Rules Committee staff came up with a very preliminary draft suggesting that a quorum could temporarily be defined as a majority of those able to respond to the calls of the House. This would occur only after the speaker has determined that a disaster has occurred and after members are unable to respond to multiple summons to the House.

In such circumstances, "it would do well to focus on physical attendance as the measuring device," House Parliamentarian Charles Johnson told the panel.

That still leaves undefined when a member is incapacitated, what comprises a catastrophe and how long this "temporary" reduced quorum should continue.

Dr. John Eisold, the attending physician to Congress, said incapacitation is a subjective judgment. As the personal doctor to members, Eisold said he would not make a statement to congressional leaders that a member is incapacitated.

"I would respect the member's wishes, even if job performance had deteriorated, and not discuss their health status," he said.

Walter Dellinger, a constitutional scholar and Duke University law professor, said any rules change must be precise enough to prevent political manipulation. "A rule aimed at safeguarding our country in extremis ought not to be drafted in a way that would permit its use by factions aiming for undemocratic results," he said.

Rep. Martin Frost, D-Texas, who in 2002 co-chaired a continuity-of-Congress working group, cited a recent situation in his own state where Democrats in the legislature fled to Oklahoma in an ultimately unsuccessful attempt to block Republicans from carrying out a redistricting plan. What would have happened, he asked, if the leaders back in Austin had changed the rules in their absence.

"There's a fine line," Frost said, between "determining a natural catastrophe and the exercise of a majority's will to reduce the number of a quorum."