Sept. 11 alerted most Americans to the grave dangers that are now facing our world. Most Americans understand that had al Qaeda possessed an atomic device last September, the city of New York would not exist today. They realize that last week we could have grieved not for thousands of dead, but for millions.

But for others around the world, the power of imagination is apparently not so acute. It appears that these people will have to once again see the unimaginable materialize in front of their eyes before they are willing to do what must be done. For how else can one explain opposition to President Bush's plan to dismantle Saddam Hussein's regime?

I do not mean to suggest that there are not legitimate questions about a potential operation against Iraq. Indeed, there are. But the question of whether removing Saddam's regime is itself legitimate is not one of them. Equally immaterial is the argument that America cannot oust Saddam without prior approval of the international community.

This is a dictator who is rapidly expanding his arsenal of biological and chemical weapons, who has used these weapons of mass destruction against his subjects and his neighbors, and who is feverishly trying to acquire nuclear weapons.

The dangers posed by a nuclear-armed Saddam were understood by my country two decades ago, well before Sept. 11. In 1981, Prime Minister Menachem Begin dispatched the Israeli air force on a predawn raid that destroyed the Iraqi nuclear reactor at Osirak. Though at the time Israel was condemned by all the world's governments, history has rendered a far kinder judgment on that act of unquestionable foresight and courage.

Two decades ago it was possible to thwart Saddam's nuclear ambitions by bombing a single installation. Today nothing less than dismantling his regime will do. For Saddam's nuclear program has changed. He no longer needs one large reactor to produce the deadly material necessary for atomic bombs. He can produce it in centrifuges the size of washing machines that can be hidden throughout the country -- and Iraq is a very big country. Even free and unfettered inspections will not uncover these portable manufacturing sites of mass death.

We now know that had the democracies taken pre-emptive action to bring down Hitler's regime in the 1930s, the worst horrors in history could have been avoided. And we now know, from defectors and other intelligence, that had Israel not launched its pre-emptive strike on Saddam's atomic-bomb factory recent history would have taken a far more dangerous course.

I write this as a citizen of the country that is most endangered by a pre-emptive strike. For in the last gasps of his dying regime, Saddam may well attempt to launch his remaining missiles, with their biological and chemical warheads, at the Jewish state.

Though I am today a private citizen, I believe I speak for the overwhelming majority of Israelis in supporting a pre-emptive strike against Saddam's regime. We support this American action even though we stand on the front-lines, while others criticize it as they sit comfortably on the sidelines. But we know that their sense of comfort is an illusion. For if action is not taken now, we will all be threatened by a much greater peril.

We support this action because it is possible today to defend against chemical and biological attack. There are gas masks, vaccinations and other means of civil defense that can protect our citizens and reduce the risks to them.

Indeed, a central component of any strike on Iraq must be to ensure that the Israeli government, if it so chooses, has the means to vaccinate every citizen of Israel before action is initiated. Ensuring this is not merely the responsibility of the government of Israel, but also the responsibility of the government of the U.S.

But no gas mask and no vaccine can protect against nuclear weapons. That is why regimes that have no compunction about using weapons of mass destruction, and that will not hesitate to give them to their terror proxies, must never be allowed to acquire nuclear weapons. These regimes must be brought down before they possess the power to bring us all down.

If a pre-emptive action will be supported by a broad coalition of free countries and the U.N., all the better. But if such support is not forthcoming, then the U.S. must be prepared to act without it. This will require courage, and I see it abundantly present in President Bush's bold leadership and in the millions of Americans who have rallied behind him.

I recognize this courage because I see it on the faces of my countrymen every day. Millions of Israelis who have been subjected to an unprecedented campaign of terror have stood firmly behind our government in the war against Palestinian terror. We have not crumbled. We have not run. We have stood our ground and fought back.

Today the terrorists have the will to destroy us but not the power. Today we have the power to destroy them. Now we must summon the will to do so.

Mr. Netanyahu is a former prime minister of Israel.