So the Petraeus-Crocker hearings are over, and we know what was obvious before they started: There will be no change in Iraq policy until the election of a new president.

But what most legislators still don't know is what policy we are pursuing or when our troops can exit.

"What's the best-case scenario where we can tell the public we can leave because of success?" asked Republican Sen. Norman Coleman, a query repeated in some form by almost every legislator at four sets of congressional hearings. "It has to do with conditions," Gen. David Petraeus answered cryptically.

Having watched much of the testimony, and met with Petraeus and Ambassador Ryan Crocker last week in Washington, I'll offer a hypothesis about what's needed.

Let's call it the "bottom-up, outside-in formula" for a responsible Iraq exit.

The purpose of the U.S. troop "surge" was to create a better security climate that would enable Iraq's warring Shiite and Sunni factions to make a deal and stabilize the country. Everyone agrees security did improve in recent months.

But the Shiite-led government of Prime Minister Nouri al-Maliki appears incapable of grand reconciliation gestures. Maliki's inept effort to re-exert control over Basra revealed both his own weakness and the continued weakness of Iraqi security forces.

So the new mantra of everyone from President Bush to conservative columnists to center-left think tanks says the solution lies with "bottom-up" Iraqi progress at local levels. Sunni tribal leaders in the provinces and in Baghdad have turned against al-Qaida and allied with U.S. forces. Some local Shiite communities have, in turn, rebuffed radical, thuggish Shiite militias like Muqtada al-Sadr's Mahdi Army.

A few of these local groups, Sunni and Shiite, have begun reaching out to one another across sectarian lines in pursuit of common interests. But the problem with the bottom-up thesis is that Iraq's central government is so weak.

Neighborhoods, towns or even provinces that have stabilized are not yet stitched into a broader political fabric. They don't fall neatly into separate ethnic enclaves — which rules out the idea Iraq could neatly split into Kurdish, Shiite and Sunni provinces.

Right now U.S. forces are necessary to prevent these quiet spots from sinking back into violence.

So the question is how to turn bottom-up security into broader Iraqi security. Crocker told Sen. Coleman frankly that there "has to be vertical integration as well as horizontal integration," meaning local secure areas must be integrated into some central Iraqi structure for that security to jell.

That leaves the United States with three choices in the near term: Pull out the U.S. troops that keep that bottom-up strategy in place and watch the violence surge again; maintain the troops and hope Iraqi elections in late 2008 and 2009 return more capable leaders than Maliki. Or, adopt an "outside-in" security strategy to complement "bottom-up."

An outside-in strategy would make a much more serious effort to persuade Iraq's neighbors to help stabilize the country.

But the missing piece of the outside-in formula is a coherent strategy to deal with Iran. President Bush last week threatened Iran if it "makes the wrong choice" in Iraq. Petraeus and Crocker criticized Iran for training and arming Shiite Iraqi militiamen. But threats alone aren't enough.

As the Basra episode clearly showed, a stable Iraq is unlikely to emerge without Iranian cooperation. When the Maliki government got in hot water in Basra, senior Iraqi Shiite officials, including a Maliki representative, rushed to Iran, where Iranian officials apparently helped broker a Basra cease-fire.

Crocker has conducted low-level talks with Iran, but the White House needs to be thinking about a broader strategic framework for the region. That, in turn, would require talks with Tehran without preconditions. There are no guarantees such talks would work, but we won't know without trying. Without a bottom-up, outside-in formula, there's no good way out of Iraq.

Trudy Rubin is a columnist and editorial-board member for the Philadelphia Inquirer. Reach her at trubin@phillynews.com.