WASHINGTON — The American military command in Afghanistan on Monday abruptly reversed its decision to classify details about the Afghan Army and police, information that it had said could pose a grave security risk if disclosed.

The data, which includes figures like the number of Afghan soldiers and what it costs to feed them, had been readily available for the past six years. But last week word leaked that the information would be kept secret going forward, a move the American command insisted was needed to safeguard Afghan and American lives.

Many in Kabul and Washington, including members of Congress, expressed skepticism about that rationale.

American officials often call the building of the Afghan security forces — a project that has cost $65 billion to date — one of the most significant achievements of the American-led coalition. Yet those forces continue to struggle against the Taliban, and about 9,500 American troops and thousands of contractors remain in Afghanistan to train Afghan soldiers and police officers and to help them battle insurgents.