But his efforts to recapture the stage were largely drowned out by a tumultuous day of street rallies, in which the three main opposition leaders marched with their followers for the first time in months. Flouting the official government message of support for Palestinian militants, they chanted, “No to Gaza and Lebanon, I will give my life for Iran.”

Image Iranian supporters of the opposition leader Mir Hussein Moussavi in Tehran on Friday. Credit... Abedin Taherkenareh/European Pressphoto Agency

Coming a day after President Obama announced a revised missile defense system that aims to check Iran’s military ambitions, the rallies underscored the continuing vitality of the domestic opposition movement, which has rejected the election as fraudulent and fiercely criticized the violence that followed it.

In a striking contrast with earlier rallies, the police often stood on the sidelines as protesters faced off against huge crowds of government supporters  many of them bused in from outside the cities  and chain-wielding Basij militia members. There were reports of arrests in Tehran and the southern city of Shiraz, but no shootings or deaths, with the police apparently showing greater restraint than during earlier protests.

The protesters, ignoring stern official warnings not to use the annual pro-Palestinian rally as a pretext for demonstrations, showed up in large numbers wearing the trademark bright green color of the opposition.

When government men shouted “Death to Israel” through loudspeakers, protesters derisively chanted “Death to Russia” in response. Many opposition supporters are angry about Russia’s quick acceptance of Mr. Ahmadinejad’s electoral victory.