BAGHDAD — Worries over increased violence fueled by Iraq’s political instability have forced U.S. commanders to reconsider the pace of a major pullout this summer without overstepping a deadline to cut the military’s presence by nearly half by the end of August.

More than two months after parliamentary elections, the next government has still not been formed, and militants aiming to exploit the void have carried out attacks like Monday’s bombings and shootings that killed at least 119 people. It was the country’s bloodiest day of 2010.

The insurgent threat has prompted military officials to figure how to keep as many troops on the ground, for as long as possible, and still withdraw all but 50,000 U.S. troops by Aug. 31, as ordered last year by President Obama.

In Baghdad and Washington, U.S. officials say they remain committed to the deadline, which would only be pushed back by Obama to deal with a severe worsening of Iraq’s security.

But the start of what the top U.S. commander in Iraq, Army Gen. Ray Odierno, called the withdrawal “waterfall” – sending home large numbers of troops in a swift period over the summer – could be affected.

In a January interview with The Associated Press, Odierno said he hoped to start withdrawing as many as 12,500 troops a month, starting in May, to meet the August deadline.

At the time, there were 96,000 U.S. troops in the country. As of last week, that number was 92,000, meaning an average of 10,500 a month would have to be pulled out.

But three U.S. officials in Baghdad and a senior Pentagon official said that the “waterfall” is now expected to begin in June at the earliest, instead of May. All said that was due to ongoing concerns about whether the political impasse would lead to violence, and spoke on condition of anonymity to discuss the process more candidly.

“From a military perspective, the best way for us to maintain security is to hold as many forces on the ground until we need to redeploy them,” said one of the senior officials in Baghdad. “It’s really prudent, given the political conditions are unsettled, for (Odierno) to wait as long as he can.”

At the Pentagon, “there’s been a renewed focus on Iraq lately,” said the senior military official there. He said all options were being considered, including later delays, adding that “we need to get out in an appropriate way … not completely tied to a time line.”