WASHINGTON -- The United States will wage a "long and sustained" war against terrorists and the states that support them, while warplanes will patrol the skies over vulnerable cities at home, senior U.S. officials said yesterday.

As they laid out the still-unfolding strategy for winning what President George W. Bush dubbed "the first war of the 21st century," officials painted a stark picture of air and missile strikes, covert operations by special forces or even a full-scale ground war if needed.

Americans also will face extraordinary security measures -- such as armed guards on airliners and the grim reality that the government would order combat jets to shoot down any hijacked airliners that are turned into missiles.

Already, pairs of F-16 and F-18 warplanes are patrolling high above Washington and New York, maintaining a vigilant combat air patrol that is expected to remain, if not indefinitely, at least for the foreseeable future.

"You don't do it with just a single military strike, no matter how dramatic," deputy defense secretary Paul Wolfowitz said yesterday. "It's not just simply a matter of capturing people and holding them accountable, but removing the sanctuaries, removing the support systems, ending states who sponsor terrorism."

U.S. forces abroad, on the highest state of alert -- "Defense Condition Delta" -- have been told to be ready for "dangerous work, . . . in the days ahead," by Defense Secretary Donald Rumsfeld.

But White House spokesman Ari Fleischer noted yesterday that the enemy is different this time: "This enemy is nameless; this enemy is faceless; this enemy has no specific borders; this enemy does not have airplanes sitting on tarmacs. It does not have ships that move from one port city to the next."

For decades, American presidents have been loathe to commit to military operations overseas unless the United States possessed overwhelming force and could minimize the risks of significant U.S. casualties.

This "different kind of war" may force a refashioning of that doctrine, if only because flushing out small cells of terrorists in remote locations may preclude huge operations. "Our nation's military is capable of carrying out whatever mission is assigned to it to conquer any enemies," Mr. Fleischer said.

That change in doctrine seems certain to apply defensively as well.

Although anti-aircraft missiles sited to protect the White House (and presumably the Pentagon) have existed for years, there was no effort to try to bring down the Boeing 757 that slammed into the Pentagon. As further details emerged yesterday, that seemed even more remarkable: The terrorist pilots twice circled the capital before flying down the Mall past the White House and turning across the Potomac to crash into the Pentagon.

With combat air patrols in the skies, it now seems clear that the U.S. government is prepared to order civilian airliners shot down if they pose a threat.

Indeed, sabre rattling seems everywhere in Washington this week; few seem ready to worry about the risks, either of losses or escalation.

Senator John McCain, a highly decorated Viet Nam combat flyer, said: "I think the United States is in a long twilight struggle against these forces of evil . . . and I believe that it may take a lot of time, a lot of American treasure, and perhaps some American blood."