WASHINGTON, Feb 6 (Reuters) - The Pentagon said on Friday it was still on track to send three additional combat units to Afghanistan by midsummer, despite a debate within the Obama administration about the timing of the deployment.

President Barack Obama had been widely expected to approve as early as this week a plan to deploy up to 17,000 combat troops as part of an anticipated buildup that could nearly double the U.S. force in Afghanistan to about 60,000 troops over the next 12 to 18 months.

The additional forces are needed to combat an intensifying insurgency by the Taliban and other militant groups.

Defense Secretary Robert Gates has spoken publicly about sending two additional combat units by the end of spring and a third by midsummer.

"That is still the goal," Pentagon spokesman Bryan Whitman told reporters.

There are currently 36,000 U.S. troops in Afghanistan, including 17,000 who operate as part of a 50,000-strong NATO force.

But officials, who spoke on condition of anonymity, said the plan for Afghanistan was still being debated in the White House National Security Council, where it has come under scrutiny at a time when the Obama administration is also considering options for withdrawing forces from Iraq where there are 144,000 U.S. troops.

The Obama administration is separately conducting a wide-ranging review of U.S. strategy in Afghanistan.

Pentagon officials say the expected buildup in Afghanistan would have to be coordinated with the drawdown of forces from Iraq because of the strains both conflicts have placed on the structure of the U.S. military.

"We need to get troops to Afghanistan soon because the spring fighting season begins in April. But there has been concern that a large initial deployment could force their hand in Iraq," said one official familiar with the debate.

Pentagon officials have provided Obama with a set of options for withdrawing U.S. forces from Iraq, including one that keeps to the 16-month timetable for the drawdown of combat troops that was his campaign centerpiece.

But no decisions on Iraq have been made and the ongoing debate has led to speculation the initial Afghan deployment had been delayed, an assertion the Pentagon was quick to reject.

"You're looking for something that's not there yet," Whitman told reporters. "I don't see this as a postponing of anything. This is not on a particular timeline."

"We're certainly not in a window that endangers that desired goal at this point," he said.

Whitman said U.S. military planners could deploy forces to Afghanistan without drawing down in Iraq but added that could require the unwelcome option of reducing the time at home between combat missions, which the Pentagon wants to avoid.

"There's any number of force management tools that you can use to maintain the level of effort, if you decided to hold in one (theater) and increase in the other. Some of those options aren't particularly attractive," Whitman said. (Reporting by David Morgan; Editing by Peter Cooney)

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