(Updates with Maliki call, poll reaction)

WASHINGTON, May 7 (Reuters) - After another bloody weekend for U.S. troops in Iraq, the White House said on Monday Americans should brace for more casualties in the push for greater security in Baghdad.

Eight U.S. soldiers were killed on Sunday in roadside bomb attacks, following an April in which more than 100 died.

White House spokesman Tony Snow said the deaths were attributable to efforts to bring security to Baghdad as part of a 3-month-old troop buildup.

"We are getting to the point now with the Baghdad security plan where there is going to be real engagement in tougher neighborhoods and you're likely to see escalating levels of casualties," Snow said.

"We've known that, been saying it all along. We're getting into some of the grittiest security operations," Snow said.

U.S. President George W. Bush spoke with Iraq's Shi'ite Prime Minister Nuri al-Maliki on Monday morning, discussing regional relations and outreach to groups within Iraq, Snow said.

More than 3,300 Americans have died in the 4-year-old Iraq war. Public disapproval over the handling of the war has helped push Bush's ratings to the lows of his presidency.

A Newsweek magazine poll on Saturday said Bush's approval rating had fallen to 28 percent, an all-time low for him in that survey, and 62 percent believed Bush's recent actions in Iraq showed he was stubborn and unwilling to admit mistakes.

Snow dismissed the Newsweek poll as skewed because it surveyed Americans who leaned more towards Democrats than Republicans.

"The president certainly understands that Americans don't like war. He doesn't like war either, but he also does not like the alternative," he said.

Bush, who is locked in a battle with Democrats over legislation to fund the Iraq war, has emphasized that withdrawing troops too early would mean failure.

Last week he vetoed a Democratic bill that would have forced him to start withdrawing U.S. troops from Iraq this year, legislation that al Qaeda's No. 2, Ayman al-Zawahri, said in a Web video on Saturday was proof of Washington's defeat.

Bush has vowed never to accept a withdrawal deadline and his aides are engaged in negotiations with key legislators on Capitol Hill trying to find an agreement that would provide $100 billion for the Iraq and Afghanistan wars.

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