ASHINGTON, Sept. 16 ・A day after proclaiming flatly that the nation was "at war," President Bush and his senior advisers took pains to warn Americans today that it would be a war unlike any other, fought in the shadows, testing the patience of the public and leaders alike, but that nations failing to join the crusade would face the "full wrath of the United States," as Vice President Dick Cheney put it.

"This is a new kind of evil," Mr. Bush said at the White House after a weekend war council with senior aides at Camp David, "and we understand, and the American people are beginning to understand, this crusade, this war on terrorism, is going to take a while, and the American people must be patient."

"We will rid the world of the evil- doers," Mr. Bush said, adding a moment later, "They have roused a mighty giant, and make no mistake about it, we're determined."

As if to acknowledge the surreal sense of both tumult and Sunday calm in the capital, Mr. Bush added: "Oh, there will be times when people don't have this incident on their minds; I understand that. There'll be times down the road where citizens will be concerned about other matters, and I completely understand that. But this administration, along with those friends of ours who are willing to stand with us all the way through, will do what it takes to rout terrorism out of the world."

In his first public remarks since Tuesday's terrorist attacks, Mr. Cheney offered chilling new details today, saying that Mr. Bush had authorized military pilots to intercept and shoot down any commercial airliner that tried to penetrate airspace over Washington after the attacks on the Pentagon and World Trade Center towers. The Pentagon scrambled fighter jets to track a hijacked jetliner headed toward Washington, but the plane crashed in Pennsylvania, possibly after a struggle between passengers and the hijackers.

Officials said that Ronald Reagan National Airport, just across the Potomac River in Virginia, would not reopen soon, and some suggested that it be permanently closed to commercial air traffic because its flight paths cross within seconds of virtually all important government buildings and monuments.

Speaking on the NBC program "Meet the Press," Mr. Cheney echoed other senior officials in declaring that nations harboring terrorists like Osama bin Laden, the prime suspect in last week's attacks, would face "the full wrath of the United States."

At the same time, Mr. Bush and Secretary of State Colin L. Powell made it clear that Washington was reaching out to an unlikely range of potential allies, including Pakistan, India and possibly even Iran, which has been listed by the State Department as the world's most active sponsor of state-supported terrorism.

Secretary Powell said that United States officials expected to contact Taliban leaders in Afghanistan to demand they expel Mr. bin Laden's organization, which has been operating there for several years. "They must help us destroy this organization," Secretary Powell said.

Mr. Cheney warned that the coming conflict would have to be fought "in the shadows" with the help of unsavory intelligence sources, and despite a 1976 executive order banning assassinations by the government, said he saw nothing to prevent the United States from killing Mr. bin Laden if it could find him. Asked by the "Meet the Press" moderator, Tim Russert, if he would like Mr. bin Laden's "head on a platter," Mr. Cheney replied, "I would take it today."

As Wall Street nervously prepared to reopen on Monday, Mr. Cheney said the country "quite possibly" could experience war and recession at once. But he also said, "I would hope the American people would, in effect, stick their thumb in the eye of the terrorists and say they've got great confidence in the country, great confidence in our economy, and not let what's happened here in any way throw off their normal level of economic activity."

In other ways, change was clearly in the wind. Attorney General John Ashcroft met with leading legislators to seek support for an emergency package of antiterrorism bills, including one that calls for a significant expansion of the Justice Department's ability to use wiretaps in cases of suspected terrorism or espionage. Under the proposal, investigators would have broad authority to conduct so-called roving electronic surveillance of suspected terrorists as they moved from one telephone or computer terminal to another. Other elements call for new authority to fight money-laundering and punish those who harbor terrorists.

Secretary of Defense Donald H. Rumsfeld, speaking on "Fox News Sunday," said simply, "It's a new kind of war," adding: "It will be political, economic, diplomatic, military. It will be unconventional, what we do."

Mr. Cheney, Mr. Rumsfeld and Mr. Powell all said, in the clearest terms yet, that evidence pointed to Mr. bin Laden and his Al Qaeda organization as responsible for last week's attacks. But speaking in phrases that echoed each other and were clearly coordinated, they also emphasized that other groups, including the Islamic Jihad in Egypt and a terrorist cell in Uzbekistan, are also a threat.

"There is no question but that he is a prime suspect," Mr. Rumsfeld said. "The Al Qaeda organization, however, is a large, multiheaded effort that probably spans 60 countries, including the United States, and it is much bigger than one person, and the problem is much broader."

The Navy destroyer Cole, damaged in Yemen last October in a terrorist attack linked by military officials to Mr. bin Laden, was quietly reactivated on Friday in Pascagoula, Miss., the Navy said.

Mr. Cheney went out of his way to say that so far American intelligence had turned up no evidence of Iraqi involvement in the attacks last week, and Secretary Powell said that officials were exploring whether Iran, which the United States severed relations with in 1980, could be helpful in fighting this new war.

The administration has drafted a special message to the Iranian government saying that Iran can join the fight against terrorism but to do so must change its policies, a senior administration official said today.

But a decision had not yet been made by Secretary Powell or the national security adviser, Condoleezza Rice, to send the message, the official said.

The message says that the Iranians cannot be selective about which terrorists they oppose. Iran considers the Taliban a bitter enemy but at the same time is a major backer of other terrorist groups, like the Hezbollah in Lebanon.

In Iran, Tehran's mayor, Morteza Alviri, and Mohammad Atrianfar, the head of Tehran's city council, sent a letter of condolence to Mayor Rudolph W. Giuliani of New York, the first government-to-government communiqu・in two decades, a gesture that hinted of possible Iranian cooperation against terrorism.

"Undoubtedly, this act is not just against New Yorkers, but all humanity," the letter said, according to reports on the front pages of many of today's newspapers in Tehran.

In his comments on the White House lawn today, Mr. Bush emphasized his discussions with three nations: Pakistan, India and Saudi Arabia. He noted that the general who took over in Pakistan not long ago, Pervez Musharraf, has been particularly helpful, and administration officials say that a delegation is being sent to Pakistan with a list of specific requests. He did not detail them.

"The leader of Pakistan has been very cooperative," Mr. Bush said. He also had kind words for the leader of Pakistan's avowed enemy, India. The National Security Council said today that Mr. Bush spoke this morning with Prime Minister Atal Behari Vajpayee of India, who offered condolences and a promise of support. India today turned over much of the intelligence it has gathered about the Taliban and other terrorist groups, including some it blames for terror on its own territory, officials said.