Under fire from stressed travelers and steamed lawmakers, the Bush administration pledged on Tuesday to be "very flexible" in eliminating the current passport backlog and enforcing new passport rules next January.

Senators peppered Maura Harty, assistant secretary of state for consular affairs, about the delays in processing passports, a situation that postponed or ruined the travel plans of thousands of Americans. The delays were due largely to a post-Sept. 11 security change that, for the first time, requires U.S. citizens to present a passport when flying to Canada, Mexico, or the Caribbean.

Sen. James Webb, D-Va., questioned how the departments of State and Homeland Security plan to cope with an even greater demand for passports in January, when the Bush administration plans to require them for land and sea crossings to those neighboring countries as well.

Harty took blame for the current backlog, and said the government's soon-to-be announced plan for land and sea crossings "will be very flexible." She did not specify whether the flexibility would come with regard to the January date, or through border crossing procedures.

The administration has insisted, as recently as last week, that it would go ahead with the January passport requirement despite the risk of more backlogs.

Senators remained skeptical.

"We want to know who's accountable and why this mess has happened," said Sen. Bill Nelson, D-Fla., who chaired the Senate Foreign Relations subcommittee hearing.

"This cannot be allowed to happen again," said Sen. Norm Coleman, R-Minn.

Harty said the delay came from "a miscalculation on the size of the surge" in passport demand and partly blamed Hurricane Katrina, which reduced the capacity of the passport office in New Orleans.

"I take responsibility for it," Harty said.