WASHINGTON — The White House sought to reassert control over the public debate on the Afghanistan war on Monday as political reaction to the disclosure of a six-year archive of classified military documents increased the pressure on President Obama to defend his war strategy.

On Capitol Hill, leading Democratic lawmakers said the documents, with their fine-grain portrayal of a war faring even more poorly than two administrations have previously portrayed, would intensify congressional scrutiny of Mr. Obama’s policy.

“Those policies are at a critical stage, and these documents may very well underscore the stakes and make the calibrations needed to get the policy right more urgent,” Senator John Kerry, a Massachusetts Democrat who heads the...