CAIRO — Just getting thousands of protesters into the streets of Tehran despite fears of beating and arrest was a victory for the Iranian opposition, but the first protest in nearly two weeks also displayed the movement's limitations.

Iran's clerical rulers are betting with no clear leader and security forces bearing down, such dramatic shows of discontent will be hard to sustain.

What the thousands of mainly young men and women marching Thursday did have going for them was determination. When security forces charged, beating them with batons, protesters scattered, regrouped nearby and resumed their chants of "death to the dictator." They pumped their fists or flashed victory signs in the air, dashing for cover when police fired clouds of tear gas.

One witness account posted online Friday described a girl shoving a police officer who grabbed her then punching him in the stomach before escaping. Protesters blocked roads with chunks of concrete, trying to stop the motorcycles of the feared Basiji militiamen from reaching the crowds.

There also were signs of support from those who didn't join in. Amid the turmoil, shopkeepers and residents let fleeing protesters slip into their homes or shops. Motorists blasted car horns as a sign of their backing for the protesters.

It was a powerful morale booster for activists who have been living in fear since Iran's clerical leadership cracked down and put an end to the massive street rallies that erupted in the wake of the country's June 12 presidential elections.

Notably missing, however, was the man whose name many of the demonstrators chanted: Mir Hossein Mousavi, the pro-reform candidate they say was cheated of victory in the elections by vote fraud. Mousavi and other mainstream reform politicians appear to have had little role in organizing the demonstrations.

Mousavi in part might have feared arrest if he came out in support of more street demonstrations. But he also has given signals the past week that the time for protests has past, hinting he could start a political party to press his demands for change within the system.

The election dispute has demonstrated that many Iranians are unhappy with their government — but there is no consensus on how to harness that anger and to what end. Some are looking for dramatic change in Iran's cleric-ruled Islamic Republic — even its removal — but politicians like Mousavi come from the heart of the system and want to preserve it with some reforms.

"There's still an opposition movement, but it's not united," said Alireza Nader, an Iran specialist with the Washington-based RAND Corp. think tank.

Mousavi and most pro-reform leaders see the protests as leverage against the clerical leadership and hardline President Mahmoud Ahmadinejad, but they don't want anger on the streets to get out of control, he said.

"They don't want to press things to far. They don't want to bring down the system," Nader said.