Obama, Obama...

Iran’s beleaguered opposition movement struggled to reassert itself on Wednesday, as tens of thousands of protesters braved police beatings and clouds of tear gas on the sidelines of a major, government-sponsored anti-American rally.

The protests — in Tehran and several other cities — were the opposition’s largest street showing in almost two months, and came on the 30th anniversary of the takeover of the United States Embassy in 1979, a day of great symbolic importance for both Iran and the United States. Although a huge deployment of police beat back and scattered many of them, the protesters took heart at their ability to openly challenge the government despite a stream of stark warnings from all levels of Iran’s conservative establishment.

Even some government authorities seemed to grudgingly concede that the opposition had — for the first time — disrupted the annual anti-American rally. The official IRNA news agency reported in midafternoon that “rioters,” many wearing the opposition’s signature green color, had gathered in front of its offices on Valiasr Street chanting “Death to the dictator” and other antigovernment slogans.

At the same time, a new theme emerged, with many protesters declaring their impatience with President Obama’s policy of dialogue with the Iranian government. Many could be heard chanting, “Obama, Obama — either you’re with them or you’re with us,” witnesses said.

Mr. Obama released his own statement on Wednesday to mark the anniversary of the embassy takeover, repeating his appeals to move beyond the two countries’ mutual distrust. The statement expressed sympathy for Iran’s opposition movement and suggested that time was running out on a United Nations-backed plan aimed at averting a showdown over Iran’s nuclear ambitions.

“The world continues to bear witness to their powerful calls for justice and their courageous pursuit of universal rights,” the statement said of the Iranian people. “It is time for the Iranian government to decide whether it wants to focus on the past, or whether it will make the choices that will open the door to greater opportunity, prosperity, and justice for its people.”

Protesters openly flouted the day’s official anti-American message, with about a thousand people, many wearing clothing and accessories in the opposition’s signature bright green color, gathering outside the Russian Embassy in Tehran and chanting, “The real den of spies is the Russian embassy.”

The American embassy has been called the “den of spies” in Iran for decades. But many opposition supporters were angered by Russia’s early acceptance of Mahmoud Ahmadinejad’s disputed victory in Iran’s June presidential elections.