BAGHDAD - The U.S. and Iraqi militaries have tentatively agreed to keep a joint base on the edge of Baghdad's Shiite slum of Sadr City, maintaining an American presence in a strategic area even after the June 30 deadline for U.S. combat troops to pull out of the capital.

The base - Joint Security Station Commanche - is one of about 14 joint facilities that U.S. officials say privately they would like to keep in flash-point neighborhoods after the deadline. Commanche is the most significant because it controls the area where Shiite extremists poured rocket fire onto the Green Zone during the last major fighting in the city in 2008. Extremists are believed to be trying to regroup in the area.

"We consider that critical," said Brig. Gen. Mike Murray, a deputy commander of U.S. forces in Baghdad.

But keeping the base after the end of the month would require approval from the Iraqi government, which is under pressure to show its supporters that the United States is sticking to the withdrawal schedule in the U.S.-Iraq security agreement.

The pact, which took effect Jan. 1, specifies that combat troops must withdraw, though not necessarily advisers and trainers working alongside Iraqi forces.

The plan to maintain a few joint bases reflects an attempt to meet the overall goal of the withdrawal plan without giving Shiite and Sunni extremists an opportunity to regain a foothold in parts of the city as the Iraqis assume more responsibility.

The status of the troops left behind in Baghdad has been kept vague, probably to avoid embarrassing the Iraqi government, which has told its people that all combat forces will be out on time.

Regardless of their formal status, all U.S. troops in Iraq are armed and trained to fight. U.S. officials have declined to say how many troops would stay behind.

A series of deadly bombings in April and May cast doubt on Iraqi capability to maintain security and raised fears of a resurgence in violence after the Americans withdraw. And just yesterday, seven people were killed and 28 wounded when a bomb exploded in a tea shop in west Baghdad.

Iraqi government officials could not immediately be reached for comment on the plan to keep the joint base on the edge of Sadr City. But Firyad Rawndouzi, a member of the parliament's security and defense committee, said some "unstable areas" might require "U.S. support" after June 30.

Keeping any U.S. troops in Baghdad is likely to draw criticism that the Americans are failing to live up to their commitment to leave the country by the end of 2011, as stipulated in the agreement.

Followers of the anti-American Shiite cleric Muqtada al-Sadr opposed the security accord when it was approved last year, saying it had loopholes for the United States to avoid the withdrawal timetable.

Sadrist lawmaker Baha al-Aaraji said this week that "the coming days will prove our reading of the agreement" that the "occupation forces will not withdraw from Baghdad."

Murray said he believed that insurgents would use the period after June 30 to test the capabilities of the Iraqi security forces in Baghdad.

"I expect violence to increase so they can make claims they chased us out of the cities," he said as U.S. troops tore down blast walls and prepared to hand over another joint security station in eastern Baghdad.

Violence has declined dramatically over the last two years since the Unitged States sent tens of thousands of extra troops to Iraq, deploying them to live with Iraqi forces in small neighborhood outposts in a bid to protect civilians and stem support for the militants. A U.S.-funded Sunni revolt against al-Qaeda in Iraq and a Shiite militia cease-fire also boosted security gains.