(edits)

By Paul Tait

BAGHDAD, June 6 (Reuters) - The final extra U.S. brigade in a security crackdown to prevent all-out civil war in Iraq is unlikely to be fully operational for up to two months, the U.S. military's top spokesman in Iraq said on Wednesday.

Military and civilian deaths have increased as thousands more U.S. and Iraqi troops are deployed in Baghdad but U.S. commanders say success cannot be judged until all five brigades are in place.

Car and suicide bombings remain an almost daily occurrence. In Baghdad, two car bombs exploded about two minutes apart in a busy Shi'ite district, killing at least seven people and wounding 25 others, police said.

The U.S. military said three American soldiers were killed in Iraq in separate explosions on Wednesday and a U.S. soldier died of gunshot wounds on Tuesday.

Four of five extra U.S. brigades are fully operational in the last-ditch bid to stop full civil war between the Shi'ite majority and Sunni minority, which ruled under ousted dictator Saddam Hussein.

That deployment will be completed "within the next couple of weeks", military spokesman Brigadier-General Kevin Bergner said.

"As we have seen with our other forces in the fight, once they're in position, they may take another 30 to 60 days to fully establish themselves with their Iraqi counterparts and the people in those sectors," Bergner told a news conference.

The commander of U.S. forces in Iraq and the U.S. ambassador are due to deliver a progress report to President George W. Bush in September as Bush comes under pressure to show progress in the unpopular war or set a timetable for a troop withdrawal.

Their assessment will focus on the progress of the security crackdown, which is designed to buy time for the government of Prime Minister Nuri al-Maliki to meet a set of political targets set by Washington aimed at promoting national reconciliation.

General David Petraeus, commander of U.S. forces in Iraq, has said his September report with ambassador Ryan Crocker will be a "forthright snapshot" of the situation in Iraq.

The full effects of the security plan may not be felt until the end of August but Bergner stressed the final brigade would still have an impact as it works towards full readiness.

PROGRESS GRADUAL

The military said this week it controls only about a third of Baghdad's 457 neighbourhoods almost four months into the crackdown.

U.S. military deaths have also hit their highest levels in more than two years. Commanders have said this was anticipated because their troops have become more visible as they conduct more operations and move out of bases into combat outposts.

A total of 127 U.S. soldiers died in May, the third-highest monthly total since the start of the U.S.-led invasion to topple Saddam in March 2003. June has begun at a high rate.

In its first two months the crackdown helped significantly reduce the number of targeted sectarian killings between Shi'ites and Sunni Arabs but civilian deaths spiked by 29 percent to almost 2,000 in May, the highest level since the crackdown began.

Bergner said local commanders had reported that progress was being made despite the rises in civilian and military deaths.

"Their collective sense is that the trends in Baghdad are better now than they were, certainly in January or February.

"As we make progress, it will not be like flipping a light switch. It will be gradual, it will be nuanced, it will be subtle."

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