WASHINGTON – Inside the Pentagon, Defense Secretary Donald Rumsfeld had just raced to his office after hearing of the World Trade Center attack. On a house porch a little more than a mile away, Ralph Banton, 79, was enjoying a crystal-clear morning.

Then Banton heard a jet flying directly overhead, very low.

“It sounded like it was jetting instead of slowing down,” he said.

Seconds later, American Flight 77, hijacked while carrying 64 people from Washington to Los Angeles, tore into the side of the Pentagon in a shocking terrorist attack aimed at the building that represents America’s military power worldwide.

The Pentagon burst into flames, sending a huge cloud of smoke up into the blue sky, visible for miles. And a part of the western side of the five-sided building in suburban Arlington, Va., collapsed.

By Tuesday night, officials were still fighting the fire and were not sure how many people might be dead or injured inside.

The area hit by the aircraft was under renovation, and thus some offices may not have been occupied, officials said.

Overall, 24,000 people work in the Pentagon.

“If we’re lucky … it would have been more lightly populated than normal,” said Rear Adm. Craig Quigley, a Pentagon spokesman. He talked to reporters at a gasoline station across the street from the massive building as an intense fire burned.

Local hospitals reported receiving 40 victims of the attack, with seven patients in critical condition admitted at one hospital for treatment of burns.

When the attack came at 9:40 a.m. EDT, “the whole building shook” with the impact, said Terry Yonkers, an Air Force civilian employee at work inside the Pentagon at the time. “There was screaming and pandemonium.”

On a nearby road, debris hit several cars. Cabdrivers watched, stunned, as hundreds of people poured out the doors of the huge building.

Rumsfeld was in his office when the aircraft hit on the opposite side of the building. He had just run there after hearing of the trade center attack while at a meeting on missile defense in his private dining room.