Many of Iran’s opposition supporters expected last Thursday to be a moment of climactic triumph, with calls for a vast street protest on the 31st anniversary of the country’s Islamic Revolution.

Instead, the day set off a flood of self-criticism by the opposition. The protest was disappointingly small — constrained by arrests, intimidation and simple crowd control — and overshadowed by President Mahmoud Ahmadinejad’s boasts about Iran’s nuclear program.

Now, dejected opposition supporters are re-examining their tactics and struggling to find a new catalyst for a movement that emerged with astonishing power just eight months ago, after the disputed presidential election.

“I think a failure has triggered debates and tactical analyses that have been needed for a long time now,” said a 26-year-old woman in Tehran, who attended last Thursday’s protest and many earlier ones, and who, out of fear for her safety, asked to be identified only as Saina. After the last major protest, around the Ashura holiday in late December, turned violent, she said, “It seemed like a lot of people were tired of being brutalized and continuing to go out into the streets.”

Many in the opposition have concluded that their lack of clear leadership, and their reliance on exiles who work through the Internet — factors that provided crucial resilience in the waves of brutal government crackdowns last summer and fall — may now be holding them back.

“A protest movement without a proper relationship with its own leaders is not a movement,” wrote an anonymous blogger, on a post titled “Lessons from 11 February.” “ It is no more than a blind rebellion in the streets which will vanish sooner than you can imagine.”

Although there are recognized opposition leaders, including the former presidential candidate Mir Hussein Moussavi and the cleric Mehdi Karroubi, their ability to organize protests has proven limited, and their credibility is low among many younger protesters who regard them as insufficiently aggressive. Many other leading figures have been arrested.