By Richard Cowan and Arshad Mohammed

WASHINGTON, July 13 (Reuters) - Despite the U.S. debate about a withdrawal of combat forces from Iraq, many lawmakers and analysts assume a large force would stay to protect Iraq's borders, train Iraqis and conduct counterterrorism operations.

Since their push began early this year to withdraw combat troops from Iraq, U.S. congressional Democrats mostly have avoided estimating the size of the force that would remain at the end of the redeployment they envision.

But some Democrats, who won control of Congress in last November's elections largely on a pledge to bring U.S. troops out of Iraq, admit they assume a sizable number would stay.

"The fact is I don't know how many troops will be there. I've heard anywhere from 20,000 -- and now I've got, this is the highest number I've heard -- to 70,000," said Senate Majority Leader Harry Reid, a Nevada Democrat, when asked about troop strength if a Senate withdrawal plan was enacted.

On Wednesday, House of Representatives Armed Services Committee Chairman Ike Skelton, a Missouri Democrat, was asked how many troops would be left behind if his legislation to bring combat troops out of Iraq by April 1 was enacted.

"I think it would be wrong for me to spell out the exact number of troops," Skelton told reporters. "I leave that as a military decision ... because I am not a general, nor am I the secretary of defense."

Skelton noted the residual missions contemplated by his legislation included "the training, equipping of the Iraqis, the force protection as well as protection of our diplomats and embassy and counterterrorism activities."

There are now about 158,500 U.S. forces in Iraq, reflecting the roughly 30,000 increase as part of the "surge" ordered by U.S. President George W. Bush in January.

Rep. James Moran, a Virginia Democrat and a leading voice in the House for withdrawing troops, said he was hoping for a withdrawal of about 100,000 U.S. troops by April.

But he acknowledged in an interview with Reuters that even if Skelton's bill became law, the Pentagon might interpret it in a way that could result in a more robust U.S. force staying in Iraq after April.

Noting that those troops had to be supplied, he said, "That's where the problem has been" with soldiers coming under attack while delivering supplies.

'FINE PRINT'

U.S. President George W. Bush gave no sign on Thursday he was willing to dramatically reduce the U.S. troop presence in Iraq as he unveiled a report that gave a mixed picture, at best, of Iraqi security and political progress.

The president asked skeptics, including among his own Republican Party, to wait until a more detailed government assessment is put forward in September.

It is not clear whether the Democrats will eventually have the votes to force a change of policy. A partial withdrawal could allow them to claim they had delivered on their campaign promise to bring troops home.

"For everybody, the $64,000 question is what do you mean by get out?" said Derek Chollet of the Center for a New American Security, alluding to the debate in Congress about withdrawing combat troops by a certain date.

"Most people, when they hear that, they hear that we are getting out," he said. "But the fine print ... says we would keep enough forces in the region or in the country to do counterterrorism, to protect U.S. assets, to ensure that there isn't some sort of humanitarian catastrophe."

Jon Alterman, director of the Middle East program at the CSIS think tank in Washington, suggested that Democrats did not want to take the blame if a large withdrawal produces chaos.

Some analysts fear a total withdrawal could worsen ethnic strife as well as draw in neighboring states like Iran, Syria and Turkey, possibly producing a wider regional war.

"Many congressional Democrats are reluctant to take ownership of the Iraq issue or to have a clear alternative to the president out of a desire to avoid being saddled with the responsibility for something that might not work," he said.

"They say the president has gotten us into this and the president can get us out of it." he added. "One of the things that I find striking now is that for all of the opposition to the president's policies, we don't see a clear array of alternatives."

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