“If only …” are the two saddest words in the lexicon when it comes to U.S. policy in Iraq.

Those words come to mind with news that President Bush has named one of the Army’s smartest and most creative generals, David Petraeus, as top military commander in Iraq, just before Bush announces his “new” Iraq strategy.

Petraeus served two tours in Iraq. I had the chance to travel with and talk to him extensively there. He understood the complex political dynamics in Iraq from the get-go; as commander of the 101st Airborne Division in 2003-4, he formulated a strategy that brought stability to the large, mainly Sunni, city of Mosul.

If only the Pentagon had adapted such a strategy then, across Iraq, things might have gone very differently. Instead, the general is being given the Herculean task of trying to salvage the security situation in a devastated country.

Petraeus, who wrote a Princeton doctorate on the lessons of Vietnam, arrived in Mosul with a plan to bring security and economic revival to the local population. He used funds captured from Baath Party sources to revive factories and jobs, giving money directly to Iraqis and avoiding the use of large U.S. contractors. He set up a hiring hall for unemployed Iraqi soldiers.

He established intensive contacts with local leaders, and instructed his soldiers not to kick down doors. His strategic goal was to implement classic counterinsurgency doctrine: Clear, hold and build. This means clearing out insurgents, making the city safe for local politics and business, and rebuilding the economy, with the aim of returning control to the local population.

Sunni tribal leaders in Mosul were effusive in praising Petraeus’ policies when I visited in 2003.

Petraeus warned that the U.S. policy of disbanding the Iraqi army would alienate thousands of Sunnis with guns; he also questioned the policy of de-Baathification, which ousted thousands of midlevel Baath Party members, including many professors and doctors, and alienated the Sunni middle class.

Sadly, the Petraeus approach was not made into broader U.S. doctrine early in the occupation. In Baghdad and other heavily Sunni areas such as Anbar province, a series of commanders used heavy-handed military tactics that angered Sunni civilians and fueled the rise of insurgents.

Even in Mosul, U.S. troops were drawn down too soon after Petraeus left, and insurgents flowed back in from Anbar, where they had been hiding. In 2005, when I flew into Mosul in a helicopter with Petraeus, we had to travel around that city in a heavily armored convoy. Several of the Iraqis I had met in 2003 either had been assassinated or had fled.

Belatedly, the administration has recognized the value of a counterinsurgency doctrine. Petraeus has just supervised the issuance of a new army counterinsurgency manual, the first in 20 years.

And President Bush has announced a surge of around 20,000 U.S. troops, along with new economic aid projects, meant to help Americans and Iraqi forces “clear, hold and build” in troubled areas of Baghdad.

It sounds like too little, too late.

Given the violence in Baghdad and Anbar, and the unreliability of Iraqi forces, 20,000 more troops is hardly sufficient to make a major difference. A surge of 10,000 U.S. troops in Baghdad this fall didn’t stop the mayhem from getting worse. Nor is it clear the military can sustain a “surge” for long enough to keep the insurgents at bay.

Even more daunting, the political situation in Iraq has changed immensely from when Petraeus first arrived. Since the bombing of a holy Shiite shrine last February, the fighting in Iraq has turned into a civil war between Sunni insurgents and revenge-seeking Shiite militias. Now Petraeus must decide whether to try first to secure Sunni areas, or also go after Shiite militias.

I suspect the general will initially pursue Sunni radicals, in hopes that this will persuade the Shiite-led government to finally rein in Shiite militias. But can he get the weak prime minister, Nouri al-Maliki, to crack down on Shiite radicals such as Muqtada al-Sadr? Can Bush’s new pick for ambassador to Baghdad, Ryan Crocker, a terrific diplomat with great knowledge of the Middle East, effect Shiite-Sunni reconciliation?

We are talking near-miracles here. Petraeus is capable of adapting to new circumstances, but much is being asked of him, very late in the day. If only the Petraeus approach to fighting insurgents had become U.S. policy in 2003.