CAIRO  An important group of religious leaders in Iran called the disputed presidential election and the new government illegitimate on Saturday, an act of defiance against the country’s supreme leader and the most public sign of a major split in the country’s clerical establishment.

A statement by the group, the Association of Researchers and Teachers of Qum, represents a significant, if so far symbolic, setback for the government and especially the authority of the supreme leader, Ayatollah Ali Khamenei, whose word is supposed to be final. The government has tried to paint the opposition and its top presidential candidate, Mir Hussein Moussavi, as criminals and traitors, a strategy that now becomes more difficult.

“This crack in the clerical establishment, and the fact they are siding with the people and Moussavi, in my view is the most historic crack in the 30 years of the Islamic republic,” said Abbas Milani, director of the Iranian Studies Program at Stanford University. “Remember, they are going against an election verified and sanctified by Khamenei.”

The announcement came on a day when Mr. Moussavi released documents detailing a campaign of fraud by the current president’s supporters, and as a close associate of the supreme leader called Mr. Moussavi and former President Mohammad Khatami “foreign agents,” saying they should be treated as criminals.