“We have many intellectuals who criticize this regime from the democratic point of view,” said Mehdi Khalaji, a former seminary student in Qum and now a senior fellow at the Washington Institute for Near East Policy. “He criticizes this regime purely from a religious point of view, and this is very hurtful. The regime wants to say, ‘If I am not democratic enough that doesn’t matter, I am Islamic.’

“He says it is not an Islamic government.”

Now in his mid-80s, frail and ill, Ayatollah Montazeri has remained in his home in Qum, the center of religious learning in Iran, issuing one politically charged religious edict after another, helping keep alive a faltering opposition movement. The man whom Ayatollah Khomeini once called “the fruit of my life” has condemned the state he helped to create.

“A political system based on force, oppression, changing people’s votes, killing, closure, arresting and using Stalinist and medieval torture, creating repression, censorship of newspapers, interruption of the means of mass communications, jailing the enlightened and the elite of society for false reasons, and forcing them to make false confessions in jail, is condemned and illegitimate,” he said in one of a flurry of written comments posted on Web sites since the election.

Iran’s current supreme leader, Ayatollah Ali Khamenei, has limited religious credentials. But Ayatollah Montazeri, a marja or source of emulation, has achieved the highest standing a cleric can hold in Shiite Islam. He is also the architect of Velayat-e Faqih, or guardianship of the jurist, the foundation of Iran’s theocracy and the source of the supreme leader’s legitimacy. Indeed, when Ayatollah Khamenei was a student, Ayatollah Montazeri was one of his teachers.

“He is able to delegitimize Khamenei more than anybody else on the Earth,” Mr. Khalaji said.

Some Iran experts argue that Ayatollah Montazeri’s involvement in politics has undermined his religious credibility, and that he does not have as large a following as other grand ayatollahs. But there is evidence, others say, that the recent conflict has increased his popularity among younger Iranians who knew little of him, and that his edicts resonate with the pious masses.