By NEIL MacFARQUHAR


Ayatollah Ali Khamenei, Iran’s supreme leader, ended his prayer sermon in tears on June 19, invoking the name of a disappeared Shiite prophet to suggest that his government was besieged by forces of evil out to destroy a legitimate Islamic government.

The opposition leader, Mir Hussein Moussavi, in criticizing the government, demanded the kind of justice promised by the Koran and exhorted his followers to take to their rooftops at night to cry out, “Allahu akbar,” or “God is great.”

In the battle to control Iran’s streets, both the government and the opposition are deploying religious symbols and parables to portray themselves as pursing the ideal of a just Islamic state.

That struggle could prove the main fulcrum in the battle for the hearts and minds of most ordinary Iranians, because the Islamic Revolution, since its inception, has painted itself as battling evil. If the government fails the test of being just, not least by using excessive violence against its citizens, it risks letting the opposition wrap itself in the mantle of Islamic virtue.

“If either the reformists or the conservatives can make reference to Islamic values in a way that the majority of citizens understand, they will win, said Mohsen Kadivar, a senior Iranian religious scholar teaching Islamic studies at Duke University in North Carolina.

Perhaps most important, the outcome may determine the support the government enjoys among the ideological zealots who form the backbone of the security forces. Some Iran experts see the level of violence in the week ahead as crucial in the tug of war over Islam.

“What is really smart about Moussavi and his group is that they say they are part of the Islamic Revolution and they want to say ‘God is great’ and overthrow tyranny,” said Said A. Arjomand, a professor of sociology at the State University of New York at Stony Brook.

“It is a struggle over the appropriation of the old symbols. If the public says we want Hussein and ‘God is great’ and then the militias are told to go kill them, that will be a little hard.”

The dawn of the Shiite faith can be traced back to the death of Hussein, the Prophet Muhammad’s grandson; his killing at the hands of a larger force in 680 has infused the faith with a sense of being the underdog. Hence, both sides in Iran portray themselves as ready to be martyrs to their cause - Ayatollah Khamenei suggested it in his sermon, and Mr. Moussavi was quoted as saying that he was also ready to give his life.

The argument on both sides has stayed narrowly within the bounds of Islam, with the opposition even deftly using green, the color of Islam and the family of the prophet, as a symbol that its protests are rooted in the faith. Both sides say they are the true heirs of the revered revolutionary patriarch, Ayatollah Ruhollah Khomeini, in trying to carry out Islamic principles.

In his criticism on June 21, Mr. Moussavi avoided any direct assault against the supreme leader, instead saying the government cheated on the results of the June 12 presidential election.

“Every Muslim understands that anyone who would lie in this way is not just,” said Mr. Kadivar, the Duke professor, who was a senior adviser to the previous reformist president, Mohammad Khatami. “The basic requirement for being the supreme leader is to be just. Justice is a key point in Islamic values.”

The argument by Ayatollah Khamenei, laid out in his June 19 sermon, is that he is the spiritual guide and therefore challenging him is challenging Islam.

In the short term he probably has the more potent argument, analysts said, but sustained violence to subdue demonstrations will work against him.

“Both sides want to paint the other as responsible for the violence,” said Mr. Arjomand, adding that the opposition could not label Ayatollah Khamenei a dictator. “They don’t want to push it too far; they know they will lose because ultimately Khamenei has the better claim to being Khomeini’s heir.”

The strength of the protests is that they have remained within religion, said Roxanne Varzi, an anthropologist at the University of California, Irvine, who has studied the way the government spreads its ideology.

“It was easier to play on the discourse of the infidel versus the righteous citizen,” said Ms. Varzi, but the opposition movement adopted the whole Islamic discourse. “It is not meant to be something anti-Islamic, even for those who are secular in their practices. Because they have kept inside that structure, it is hard for the government to justify clamping down on them.”