DARRANG DISTRICT, Assam, India — On Saturday morning, Farid Ali, a farmer dressed in his best sky-blue kurta and a white prayer cap, walked quietly into his village headquarters and received devastating news.

His name wasn’t on the list.

He looked, he waited, his legs began to shake, his dry lips began to move and he prayed there had been a mistake. But his name wasn’t anywhere.

Mr. Ali’s citizenship in India, where he has lived all his life, was now in question, and he could soon be separated from his family and hauled off to a prison camp.

He is one of nearly two million people in northeast India who were told Saturday that they could soon be declared stateless in a mass citizenship check that critics say is anti-Muslim. The news arrived in small, sunlit offices across the state of Assam, where citizenship lists were posted that drew huge crowds. Many walked away shocked and demoralized; others were joyous.