WASHINGTON  President Obama said Tuesday that he would send an additional 17,000 American troops to Afghanistan this spring and summer, putting his stamp firmly on a war that he has long complained is going in the wrong direction.

The order will add nearly 50 percent to the 36,000 American troops already there. A further decision on sending more troops will come after the administration completes a broader review of Afghanistan policy, White House officials said.

Mr. Obama said in a written statement that the increase was “necessary to stabilize a deteriorating situation in Afghanistan, which has not received the strategic attention, direction and resources it urgently requires.”

At least for now, Mr. Obama’s decision gives American commanders in Afghanistan most but not all of the troops they had asked for. But the decision also carries political risk for a president who will be sending more troops to Afghanistan before he has begun to fulfill a promised rapid withdrawal of troops from Iraq.