HAVING SPENT much of the past year mired in legislative trench warfare over Iraq, advocates in Congress seeking a mandatory withdrawal of troops are now refusing to pass funding for our forces deployed in Iraq or Afghanistan.

For Congress to fail to provide the funds needed by our soldiers in the field is inexcusable under any circumstances -- but it is especially disappointing right now, coming at the very moment when Gen. David Petraeus and his troops are achieving the kind of progress in Iraq that few would have dared imagine possible just a few months ago.

We recently traveled to Iraq, where we saw and heard firsthand about the remarkable transformation that our brave men and women in uniform have succeeded in bringing about this year.

As every major news outlet now acknowledges, security has improved dramatically across Iraq since Gen. Petraeus took command and began implementing a bold new counterinsurgency strategy -- the so-called "surge." Today, rocket and mortar attacks have dropped to their lowest levels in 21 months. Car bombs and suicide attacks in Baghdad have plummeted 70 percent. Iraqi civilian casualties are sharply down throughout Iraq. And the number of U.S. soldiers killed in action has fallen for five straight months and is now at the lowest level in nearly two years.

Simply put: a year ago, al-Qaida was winning in Iraq. Now we are.

Our soldiers know they have seized the momentum in this fight.

Idealistic and innovative, they rightly recognize what has happened this year under Gen. Petraeus as one of the most extraordinary turnarounds in American military history.

As a result of the hard-won gains our troops have secured, Gen. Petraeus has been able to initiate a drawdown of U.S. forces. The first 5,000 American troops are now on their way out of Iraq, with more likely to follow in the months ahead. However, we should not have an automatic timetable for withdrawing brigades. Gen. Petraeus should decide the size of the force he needs to maintain security and keep our enemies on the run.

The success that Gen. Petraeus and his troops have achieved could provide the foundation for a new bipartisan consensus about Iraq in Washington. All of us, after all, want our troops to succeed in Iraq so that they can begin to come home with honor.

Unfortunately, too many Democrats have thus far been reluctant to welcome the reality of progress -- instead searching for ways to deny or disparage it.

In particular, Democrats have seized on the lackluster performance of the Iraqi government to insist that we should abandon Gen. Petraeus' successful strategy and withdraw far more of our troops, far faster, than he recommends.

This would be a terrible mistake.

There is no question Iraq's national leaders must do more to promote reconciliation and improve governance in the months ahead.

But the fact is, there has been enormous political progress in Iraq at the local and provincial levels thanks to the surge, as Sunni and Shiite leaders have stepped forward to fight against the extremists in their communities.

Building on these gains is going to require deft diplomacy and subtle statecraft from the United States -- not declarations of defeat.

And whatever the failings of the imperfect, fledgling democracy in Baghdad, they do not justify abandoning it to the al-Qaida fanatics and Iranian-backed terrorists who are trying to destroy it.

And make no mistake. Despite the progress we have achieved this year, there is no cause for complacency. Just as we have managed to turn failure into success in 2007, we can likewise turn success back into failure in 2008, if we are not careful.

As Brig. Gen. Joe Fil, the commander of U.S. forces in Baghdad, recently put it, al-Qaida in Iraq is now off balance, but they will come swinging back at us, if we give them the chance.

That is why Congress' failure to fund our troops is so profoundly reckless.

Nine months ago, when Gen. Petraeus took command in Baghdad, people of good conscience could disagree about whether his new counterinsurgency strategy would succeed. After so many mistakes and missteps by the Bush administration in Iraq, many Americans were understandably skeptical about the possibility of success.

Now, however, the evidence is unequivocal. The surge is working.

Rather than holding hostage the funding for our troops in the field and writing off the hard-won gains they are secured, it is time for Democrats and Republicans alike to recognize the extraordinary progress that Gen. Petraeus' strategy has achieved -- and build a new political consensus around it.

Just as we demand Iraqi leaders take advantage of the success of the surge to set aside their sectarian agendas and pursue peace, so too it is time for Congress to stop playing senseless partisan games and instead fund our troops -- who have accomplished so much -- without delay. They deserve nothing less.

Sen. John MCain is a candidate for the Republican nomination for President. Sen. Joe Lieberman is a former presidential candidate who now represents Connecticut as an independent.