To get a good idea of how the United States should respond to the attacks on the World Trade Center and the Pentagon, consider what happened to the terrorists who bombed the U.S.S. Cole as it lay in port last October in the Middle East country of Yemen.

Nothing.

A U.S. military vessel was brazenly and deliberately targeted. An investigation was launched. And … nothing. The American public barely even heard about it again.

And that's just the point. The Cole "incident" merely joined the list of other attacks carried out against the United States in recent years, including terrorist bombings in Saudi Arabia in 1995 and 1996, which also led to U.S. military casualties. Earlier (in 1992), a Yemeni hotel used by American military personnel en route to humanitarian operations in Somalia was bombed.

For nearly a decade, we've deplored these so-called "warning shots." We've wagged fingers and vowed to get to the bottom of it. And each time, the episode fades from our collective consciousness faster than a fireworks display on the Fourth of July.

Obviously, this time is different. The terror has been brought directly to our shores, delivered with a chilling and ruthless efficiency and a callous indifference to human life. The searing images of death and destruction won't disappear anytime soon.

But it's time to realize that this is what happens when you don't respond swiftly and surely to unprovoked attacks. The level of violence keeps getting ratcheted up until, finally, an outrage erupts that no one can ignore.

War wasn't declared on the United States on Sept. 11. It was declared long ago by those who believe that the United States, which spreads such dangerous notions as freedom and democracy, is a "great satan." We just didn't want to face it.

It's too soon to pin the blame definitively on our best suspect, Osama bin Laden, the exiled Saudi who heads a terrorist network from Afghanistan with the knowledge and complicity of the Afghan government. But we know he's responsible for past terrorist attacks -- actions that resemble the World Trade Center/Pentagon outrage in sophistication and audaciousness.

We know one other thing. These attacks weren't the acts of "cowards." They were the acts of warriors willing to die for their cause. These weren't the instances of "senseless" violence some have suggested they were. They were calculated acts of military aggression and should be dealt with as such.

That's why President Bush should immediately ask Congress for a declaration of war against any international group or state that participated in the World Trade Center/Pentagon attack. This would make America's resolve clear and eliminate any confusion about how to solve the problem.

We must also, as the president said, hold accountable the states that have harbored or supported these terrorists in any way. If a regime such as the Taliban in Afghanistan is found to have harbored or supported these terrorists, it should be the goal of U.S. policy to remove that regime from power by any means necessary.

And we need to protect ourselves against future attacks. This means beefing up our intelligence capabilities, which have been sorely neglected in recent years, and vastly improving our technical capabilities to monitor terrorist activities.

It also means that we need a comprehensive homeland defense policy that defends the United States not merely against the types of attacks that occurred in Washington and New York, but against other threats. These include attacks on our computer systems, our industrial infrastructure, our financial systems, and our transportation, utility and fuel networks.

In addition, we must end our complacency about the missile threat and start building a defense against ballistic missiles, which inevitably will be the next weapon of choice for terrorist states. There are 20 nations either developing or deploying ballistic missiles. They include such rogue states as North Korea, Iraq and Iran.

Do we actually believe that once these states have the ability to rain death down on millions of Americans with a missile -- producing a casualty list that would dwarf those of New York and Washington -- they'll decide not to use such an easy and devastating method of attack? They'll have no planes to hijack, no airports to sneak through.

Enough is enough. Like it or not, we're at war. Let's start acting like it.

Kim Holmes is Vice President of Foreign and Defense Policy Studies and Director of the Kathryn and Shelby Cullom Davis Institute for International Studies at The Heritage Foundation and Jack Spencer is a defense policy analyst at The Heritage Foundation, a Washington-based public policy research institute.