Vice President Dick Cheney said Monday that aggressive U.S. action is responsible for preventing new terror attacks since the Sept. 11 strikes.

"Nobody can promise that we won't be hit," Cheney said. But he credited a determined offense against terrorists abroad, improved intelligence-gathering and preventive steps at home for thwarting or discouraging terror attacks on U.S. soil.

Answering questions at a National Press Club luncheon, Cheney also said that, when President Bush and he took office in January 2001, the balance of power in government was tilted in favor of Congress.

The unpopular Vietnam War and the Watergate scandals allowed Congress to take more authority at the expense of the executive branch, Cheney said. He and the president believed it was important to "have the balance righted, if you will. And I think we've done that successfully," he said.

Democratic critics of the president and even some Republicans have questioned the administration's assertion of expanded executive power in the name of combatting terrorism. These include warrantless eavesdropping by the National Security Agency, detention of suspected terrorists without charges, expanded powers under the Patriot Act and alleged secret CIA prisons overseas.

Cheney defended the NSA's domestic eavesdropping program, which the administration calls its "terrorist surveillance program" as important in the war on terror, while conceding it was controversial.

"We have been engaged in a debate about the wisdom of the program and whether or not it's legal, but it clearly is legal, we believe. It is consistent with the Constitution."

Under the program, the NSA has been monitoring communications of Americans without obtaining warrants so long as least one of the participants is overseas and at least one is a suspected terrorist.

The program, along with "very aggressive campaigns overseas," has helped to protect the country against new terror attacks, Cheney asserted.

He was asked if the United States is winning the war on terrorism.

"I believe we are," Cheney said. "I think we've made significant progress, if you look back over the last — nearly — five years now."

"The fact of the matter is we have been safe and secure here at home," the vice president added. "That's not an accident. It didn't happen just because we got lucky."

Cheney said the biggest terrorism threat now "is the possibility of an Al Qaida cell armed with a nuclear weapon or a biological agent in the middle of one of our own cities."

Cheney defended his comment last year, often ridiculed by administration critics, that the Iraqi insurgency was "in its final throes."

He said he was referring to a series of events — including elections and the drafting and acceptance of a new Iraqi constitution — that he believes history will show to be pivotal.

But the vice president did say that he underestimated the strength of the insurgency in some of his earlier remarks.

"I don't think anybody anticipated the level of violence that we've encountered," Cheney said. He said much of the continuing violence has its roots in "the devastation" that 30 years of Saddam Hussein's iron-fisted rule "had wrought on the psychology of the Iraqi people."

Asked if there was any possibility that the military draft would be restored, Cheney said, "No, none that I can see. I'm a big believer in the all-volunteer force. I think it's produced a magnificent military."