Baghdad ? The U.S. troop surge did what it aimed: Calm Iraq down. But now, an increasing number of U.S. officials are worried that the hard-won drop in violence may be only temporary.

The fear: that Iraq may squander this period of relative calm, failing to reach the difficult political deals the surge was designed to allow – and thus setting the stage for another round of violence some day.

The worry is behind U.S. military leaders’ constant warning that Iraq’s current calm may not endure. Defense Secretary Robert Gates was the latest, saying this week that U.S. military commanders do not yet believe “our gains are necessarily enduring.”

Their concerns were underlined by a car bombing Friday night in the mainly Shiite town of Dujail, 50 miles north of Baghdad. The blast, which Iraqi officials said killed more than 30 people and wounded scores more, was the latest in a series of attacks in areas north of the capital.

Major challenges

Iraqi leaders face major challenges in the coming months, even as the effectiveness of the surge remains a hot-button topic in the U.S. presidential race.

If the Iraqis lack the necessary political skill or desire to compromise, those challenges would lay the ground for a new wave of violence.

Ironically, the Iraqi government’s newfound strength could tempt the Shiite leadership to resist calls for compromise with its rivals.

“We have to admit to shortcomings in the practice of democracy,” Parliament Speaker Mahmoud al-Mashhadani acknowledged this week. “And we are lacking a spirit of consensus.”

Exhibit A: The Iraqi government’s delay in integrating Sunni armed men into the country’s police and armed forces. U.S. officials insist the Shiite-led government of Prime Minister Nouri al-Maliki intends to do so starting next month.

About 20 percent of the armed men – many of them ex-insurgents who volunteered to join local security forces – will go into the army and police. The rest will be placed in civilian government jobs.

But there are signs the Iraqi government, which distrusts the Sunni volunteers, is dragging its feet – with potentially explosive consequences.

The U.S. puts the number of armed volunteers at about 100,000 – the overwhelming majority of them Sunnis.

Last week, about 100 Sunni volunteers held an angry protest in north Baghdad, accusing the government of discrimination and of bowing to pressure from Shiite-dominated Iran.

Many of those volunteers were members of Sunni insurgent groups who broke with al-Qaida in Iraq and joined forces with the Americans, who have been paying them for nearly two years.

The former insurgents are Sunnis who deeply resent Shiite domination of the country since the fall of Saddam Hussein five years ago – and could return to violence if they feel cheated by the Shiites in government.

The U.S. hopes to ease Sunni concerns by giving them a share of political power through new provincial elections this year. But there again is the potential for explosive anger.

Many Sunnis boycotted the last local balloting in January 2005, enabling Shiites and Kurds to win power, even in areas with substantial Sunni populations. A new round of elections could give Sunnis the political power their numbers warrant – and thus keep them from violence.

But Iraq’s parliament has been bogged down in a complex fight between Arabs and Kurds over the new election law that’s first needed. Lawmakers took up the measure again this week after their summer break – but without any sign of an early breakthrough.

The challenges lie against a backdrop of growing – if still quiet – concern that al-Maliki may lack the skills – or the desire – to manage them. The government’s success in clearing Baghdad and Basra of Shiite militias in spring and summer emboldened the prime minister, who previously had been widely dismissed as weak.

Now he’s pushing back against the Americans in talks on a new security agreement, warning Sunnis against resisting plans to take over their armed volunteers and threatening force against the Kurds.

That has stirred fears that al-Maliki is more interested in promoting Shiite interests than reaching accommodation with Sunnis and Kurds.

“What we see is very substantial progress. But that progress has by itself created a climate in which Iraqi leaders and factions feel much more secure about advancing their own cause,” said former Pentagon analyst Anthony Cordesman.

That could mean the surge that so successfully lowered violence fails at its larger goal of providing some space for political peace to flourish.