WASHINGTON (AP) – President Barack Obama planned to declare on Friday that the United States would end its bloody and costly combat mission in Iraq by late summer of 2010, but a dramatic force reduction was not expected until after the country’s national elections at the end of this year, senior administration officials said.

The president was to announce the Aug. 31, 2010, conclusion of the mission Friday morning at the Marine Corps base at Camp Lejeune, North Carolina.

Even with the end of the combat mission, three months later than Obama pledged during his presidential campaign, a force numbering between 35,000 to 50,000 Americans forces will stay behind, with the final troops not slated to leave until Dec. 31, 2011.

There were no assurances that the residual force would not be pulled into battle should Sunni Muslim insurgent holdouts or disaffected Shiite Muslims resume wide-scale fighting.

The administration officials, who spoke on condition of anonymity because the plan was not yet public, said the pace of the withdrawal would be guided by the needs of Gen. Raymond Odierno, the top commander in Iraq. They said he felt it was important to keep an adequate combat force in the country at least until national elections this December.

The officials said Obama’s order would not specify the rate of withdrawal either before or after those elections are held. During the campaign, Obama had said it would be roughly one combat brigade per month over 16 months. While the pace of withdrawal was expected to quicken in 2010, the officials refused to be specific, noting that elections in Iraq have tended to slip beyond scheduled dates.

Depending on the number of forces left behind, the military will have withdrawn between 92,000 and 107,000 American fighting personnel from Iraq nearly 7 1/2 years after the United States invaded and toppled the regime of Saddam Hussein.

According to an Associated Press count as of Thursday, at least 4,251 members of the U.S. military have died in the Iraq war since it began in March 2003, Total Iraqi deaths are unknown but number in the tens of thousands and are perhaps above 100,000.

The senior administration officials said the U.S. force that remains after the combat mission is closed out will have a threefold mission:

_To train, equip and advise Iraq forces;

_To offer force protection for both U.S. military and

civilian operations that will continue in the country, and;

_To engage in targeted counterterrorism missions either

alone or in conjunction with Iraqi troops.

The administration officials said the plan was drawn up after a month of consultations with Defense Secretary Robert Gates, Joint Chiefs of Staff Chairman Adm. Mike Mullen, Odierno and the military service chiefs. One of the officials said the plan that Obama will announce was recommended to him by Gates and Mullen on Wednesday and was driven by his Jan. 21 orders to draw up a schedule for ending the war.

In the meantime, Obama has ordered the dispatch of 17,000 more America forces to Afghanistan, to fight resurgent Taliban insurgents. As U.S. troops leave Iraq, that would free even more forces for deployment in Afghanistan. The Iraq pullout plan is “in keeping with the president’s strategic vision” and does not mean U.S. “interests in the region” will diminish, the officials said. “We are intensifying U.S. engagement.”

The president and his advisers decided on the Aug. 31, 2010 date for ending the combat mission, the officials said, based on estimates that the threat in Iraq would be acceptable by then. There has been great concern about a new eruption of violence that could tip the country back into the horrendous brutality that swept through it in the last half of 2006 through the late summer of 2007.

Officials said there was concern the national elections at year’s end could raise tensions, making it unwise to accelerate the pullout until the spring or summer of 2010.

Obama and his national security team briefed congressional leaders on the plan Thursday evening. Before the meeting, Democratic congressional leaders, House Speaker Nancy Pelosi and Senate Majority Leader Harry Reid, both questioned the need for a residual forces as large as 50,000.

“I am happy to listen to the secretary of defense and the president,” Reid said. “But when they talk about 50,000, that’s a little higher number than I had anticipated.”

Republican lawmakers were skeptical for a different reason. They were concerned that troops might be pulled out too fast and security gains sacrificed.

“While it may have sounded good during the campaign, I do think it’s important that we listen to those commanders and our diplomats who are there to understand how fragile the situation is,” said House Republican leader John Boehner.

Sen. John McCain, who disagreed with Obama on Iraq policy when they competed for the presidency last fall, said the plan would not necessarily prevent casualties. “Let’s also be realistic: Advisers in any conflict are in harm’s way,” McCain told an audience at the conservative American Enterprise Institute.

An existing U.S-Iraq agreement, negotiated under President George W. Bush, remains in force and calls for U.S. combat troops to withdraw from Baghdad and other cities by the end of June, with all American forces out of the country by the end of 2011.