Responding to catastrophes in the nation's capital could prove more challenging than elsewhere in the country, Homeland Security Secretary Michael Chertoff (search) said Tuesday, saying he was concerned with preparedness plans in the city.

Chertoff's comments, four years after the Pentagon (search) was hit by the terror attacks of Sept. 11, 2001 (search), underscored the belief that Washington remains a prime target.

During an emergency, the large federal work force would face evacuation even as the government struggled to continue operations, Chertoff told an Aspen Institute forum on homeland security and preparedness.

"An event in the District of Columbia (search) would impose challenges of a different kind than anywhere else," Chertoff said.

Asked to elaborate, he said, "I'm not meaning to suggest there's a big problem in the district. But what I am suggesting is, I think the district will be more challenging because of the larger federal footprint than most places. And therefore I think I'm particularly concerned about making sure we are constantly improving and doing the best we can to sharpen up the plan."

Chertoff noted communication failures between Homeland Security, District of Columbia police and other responders during a brief scare on May 11, when the pilot of a single-engine Cessna mistakenly wandered into restricted airspace over Washington. The Capitol and White House were temporarily evacuated during the incident, but Mayor Anthony Williams later complained that city officials weren't told about the threat until the all-clear sounded.

Williams spokesman Vince Morris said Tuesday that city and Homeland Security officials recently have been working together to make the Washington region a national model for local preparedness.

"We want to be a part of that, and we are working with the feds and also with Virginia and Maryland so we can get to that point," Morris said.

"We feel like we're in good shape, but we also feel like we should be better," he said.