One key to stabilizing Iraq isn't even in the country, but next door in Syria.

It's not just that innumerable Saddam loyalists, al Qaeda terrorists and foreign fighters have crossed the 370-mile Syrian border into Iraq over the past year. Syria also has become a safe haven for the Ba'athist Bigs pulling the strings of the attacks in Iraq.

These thugs operate with impunity while Damascus turns a blind eye. The situation has gotten so bad - and so critical to busting the insurgency - that Washington has sent at least two senior State and Defense Department delegations (along with Iraqi officials) to Damascus in the last two months.

Their blunt message to President Bashar al Assad: Address this festering problem with concrete action - or pay the consequences.

After months of tough going, Coalition forces are now making a dent in the Iraqi insurgency by pressing the offensive in places like Fallujah. (The weekend arrest of a senior al Qaeda aide certainly helps.) The death toll among the bad guys is now as high as 15,000 since the postwar fighting began, says Central Command's Gen. John Abizaid. (He estimates that 5,000 still remain.)

But ending the flow of reinforcements, cash and weapons to the insurgents is just as important as wiping out the active fighters. That's where Syria comes in.

Under the protection of Syrian Ba'athist regime, 20 to 50 former senior Iraqi Ba'ath security-service goons and Saddam aides and relatives are supervising the guerilla war back home. Some analysts say these leadership cells are more dangerous to Iraq's long-term stability than even al Qaeda's Abu Musab al-Zarqawi.

Assad has promised to cooperate with Coalition and Iraqi requests, especially on closing the border. But he has yet to produce results.

So how do we eliminate the ability of the Syrian cells to plan, direct, organize and fund (Saddam stashed at least $1 billion in Syria before the war) the bloody rebellion?

We have much more leverage with Syria than most people think. Damascus is politically isolated (except for its closest ally, Iran). And with unemployment hovering at 20 percent, Syria's economy is faltering.

If Syria fails to cooperate, Washington could ratchet up the pressure by implementing sanctions beyond those already taken under the Syria Accountability and Lebanese Sovereignty Restoration Act of 2003.

Those laws already ban U.S. exports to Syria (less food and medicine), but Washington could cut off financial dealings with Syrian banks. This would scare off much-needed foreign investment, further crippling the Syrian economy.

America could also lean on the European Union (EU) to rescind its recently-inked trade and cooperation pact with Syria. To take effect, the agreement still needs the unanimous approval in the EU parliament. London and America's "New Europe" allies should be open to reason.

And, working with Paris (yes, Paris!), we could further squeeze Damascus by acting on the regime's intransigence over U.N. Security Council Resolution 1559. The recently-passed resolution called for Syria to withdraw all 15,000-20,000 of its troops from Lebanon. (Syrian troops have been in Lebanon since the 1976 Lebanese civil war, and the government in Beirut is essentially a Syrian puppet.)

A second Franco-American resolution on Lebanon is already in the works. Security Council punitive action, such as multilateral economic sanctions for non-compliance, is certainly possible.

Damascus also risks:

•  Creating a sworn enemy in the new Iraq.
• Losing U.S. help in reviving the stalled Syrian-Israeli peace talks (Damascus desperately wants the Golan Heights back).
• Drawing U.S. military strikes against insurgent targets in Syria - always an option.

President Bush has called Syria "an unusual and extraordinary threat." He's right. Syria's a dictatorship, has weapons of mass destruction and supports terrorism in Israel through the likes of Hezbollah and Hamas.

If Syria doesn't couple words with deeds soon, Damascus should suffer appropriate consequences. We've played nicely long enough. Assad has a fateful choice to make: Take advantage of a window of opportunity for better relations with the United States and its permanent - and increasingly angry - neighbor Iraq. Or follow the likes of Saddam Hussein and the Taliban directly into the dustbin of history.

Peter Brookes is a Heritage Foundation senior fellow. E-mail: [email protected]