WASHINGTON — I've just spent 10 days traveling in the Middle East and speaking to leaders there, all of which has made one thing clearer to me than ever: While we are naturally focused on Iraq, a larger war is emerging. On one side are extremists and terrorists led and sponsored by Iran, on the other moderates and democrats supported by the United States. Iraq is the most deadly battlefield on which that conflict is being fought. How we end the struggle there will affect not only the region but the worldwide war against the extremists who attacked us on Sept. 11, 2001.

Because of the bravery of many Iraqi and coalition military personnel and the recent coming together of moderate political forces in Baghdad, the war is winnable.

The American people are justifiably frustrated by the lack of progress, and the price paid by our heroic troops has been heavy. But what is needed now, especially in Washington and Baghdad, is not despair but decisive action — and soon.

The most pressing problem we face in Iraq is not an absence of Iraqi political will or American diplomatic initiative, both of which are increasing and improving; it is a lack of basic security. As long as insurgents and death squads terrorize Baghdad, Iraq's nascent democratic institutions cannot be expected to function, much less win the trust of the people. The fear created by gang murders and mass abductions ensures that power will continue to flow to the very thugs and extremists who have the least interest in peace and reconciliation.

This bloodshed, moreover, is the predictable consequence of a failure to ensure basic security. By ruthlessly attacking the Shiites in particular over the past three years, al-Qaida has sought to provoke the dynamic of reciprocal violence that threatens to consume the country.

On this point, let there be no doubt: If Iraq descends into full-scale civil war, it will be a tremendous battlefield victory for al-Qaida and Iran. Iraq is the central front in the global and regional war against Islamic extremism.

To turn around the crisis we need to send more American troops while we also train more Iraqi troops and strengthen the moderate political forces in the national government. After speaking with our military commanders and soldiers there, I strongly believe that additional U.S. troops must be deployed to Baghdad and Anbar province — an increase that will at last allow us to establish security throughout the Iraqi capital, hold critical central neighborhoods in the city, clamp down on the insurgency and defeat al-Qaida in that province.

In Baghdad and Ramadi, I found that it was the American colonels, even more than the generals, who were asking for more troops. In both places these soldiers showed a strong commitment to the cause of stopping the extremists. One colonel followed me out of the meeting with our military leaders in Ramadi and said with great emotion, "Sir, I regret that I did not have the chance to speak in the meeting, but I want you to know on behalf of the soldiers in my unit and myself that we believe in why we are fighting here and we want to finish this fight. We know we can win it."

In nearly four years of war, there have never been sufficient troops dispatched to accomplish our vital mission. The troop surge should be militarily meaningful in size, with a clearly defined mission.

More U.S. forces might not be a guarantee of success in this fight, but they are certainly its prerequisite. Just as the continuing carnage in Baghdad empowers extremists on all sides, establishing security there will open possibilities for compromise and cooperation on the Iraqi political front — possibilities that simply do not exist today because of the fear gripping all sides.

I saw firsthand evidence in Iraq of the development of a multiethnic, moderate coalition against the extremists of al-Qaida and against the Mahdi Army, which is sponsored and armed by Iran and has inflamed the sectarian violence. We cannot abandon these brave Iraqi patriots who have stood up and fought the extremists and terrorists.

The addition of more troops must be linked to a comprehensive new military, political and economic strategy that provides security for the population so that training of Iraqi troops and the development of a democratic government can move forward.

In particular we must provide the vital breathing space for moderate Shiites and Sunnis to turn back the radicals in their communities. There are Iraqi political leaders who understand their responsibility to do this. In Anbar province we have made encouraging progress in winning over local Sunni tribal leaders in the fight against al-Qaida and other terrorists. With more troops to support them, our forces in Anbar and their Sunni allies can achieve a major victory over al-Qaida.

As the hostile regimes in Iran and Syria appreciate, failure in Iraq would be a strategic and moral catastrophe for the United States and its allies. Radical Islamist terrorist groups, both Sunni and Shiite, would reap victories simultaneously symbolic and tangible, as Iraq became a safe haven in which to train and strengthen their foot soldiers and Iran's terrorist agents. Hezbollah and Hamas would be greatly strengthened against their moderate opponents.

In Iraq today we have a responsibility to do what is strategically and morally right for our nation over the long term — not what appears easier in the short term. The daily scenes of death and destruction are heartbreaking and infuriating. But there is no better strategic and moral alternative for America than standing with the moderate Iraqis until the country is stable and they can take over their security. Rather than engaging in hand-wringing, carping or calls for withdrawal, we must summon the vision, will and courage to take the difficult and decisive steps needed for success and, yes, victory in Iraq. That will greatly advance the cause of moderation and freedom throughout the Middle East and protect our security at home.

Joseph Lieberman is an Independent Democratic senator from Connecticut. He wrote this commentary for the Washington Post.