Dozens of high-level officials joined in a White House drill yesterday to see how the government would respond if several cities were attacked simultaneously with bombs similar to those used against U.S. troops in Iraq.

White House homeland security adviser Frances Fragos Townsend and the Homeland Security Council that she heads mapped out in advance a massive disaster involving improvised explosive devices, or IEDs. The attack targeted 10 U.S. cities, both large and small, at the same time, said a senior administration official who spoke on the condition of anonymity.

Townsend presided over the three-hour exercise, which brought the government's top homeland security officials to the Eisenhower Executive Office Building next to the White House. All Cabinet agencies were represented by their secretaries or other high-ranking officials, with about 90 participants in all, White House spokesman Scott Stanzel said.

Stanzel said the drill revealed gaps in the government's ability to respond, but also showed that there have been many improvements since Hurricane Katrina. The storm exposed federal inadequacies when it devastated the Gulf Coast in 2005. For instance, coordination with state and local authorities and the ability to get federal resources in place quickly -- key missteps after Katrina -- appeared much better now, Stanzel said.

President Bush went on a bike ride yesterday morning and did not take part in the test.

The IED attacks are common in Iraq, but Stanzel said the test was not inspired by new intelligence or any increased chatter about terrorists' desire to use IEDs inside the United States.

This was the administration's fourth such "tabletop" exercise since the first in December 2005. That exercise focused on an avian flu pandemic.