CAIRO » As hundreds fled the advancing armored cars of riot police officers, Mohamed Mokbel ran forward.

A veteran of two years of violent streets protests, he pulled on his gas mask and charred protective gloves for another long night at his current vocation: throwing tear gas canisters back at the riot police.

"Whenever people lose hope, the clashes grow worse," Mokbel, 30, said on a break from the fighting Friday night outside the presidential palace. "But the people in power are still acting like there is no crisis, still firing more gas," he said, "so I am going back in."

Two years after the ouster of President Hosni Mubarak, waves of increasingly violent street protests have decimated tourism, slashed foreign investment, increased poverty and dashed hopes of a return to stability. In the past two weeks, more than 50 people have died in the clashes. Egypt’s top general raised the specter of a "collapse of the state" if civilian leaders failed to restore order. And the interior minister warned that armed militias could take over if his forces gave way.

But behind the mayhem bedeviling the new government are street activists like Mokbel, who burst into politics around the time of the Arab Spring revolt against Mubarak and say they are still fighting for its democratic goals. Alienated from Egypt’s new Islamist leaders or their rivals in the opposition, street protesters have risen up again and again to check perceived grabs for power, whether by the interim military rulers, the elected president or his Islamist allies.

Now, while elite politicians tussle over matters of ideology or provisions of the constitution, street protesters like Mokbel say they are carrying on the fight that kindled the original revolt, a battle against Mubarak’s abusive and unaccountable security services. Two years later, they note, the security forces are still largely intact, and reports of torture, extortion and excessive force continue.

Their street war between protesters and the police presents a double-edged challenge to President Mohammed Morsi, a former leader of the Muslim Brotherhood who had been jailed without trial under Mubarak. Brotherhood leaders close to Morsi say he does not yet fully control the Interior Ministry. Its officers make no secret of their hostility to the Islamists, and Brotherhood leaders say that the new president is struggling to win the ministry’s trust in order to tame it.

But many in the street have turned against Morsi in part because that they believe that he has sided with the security forces. Activists like Mokbel say they fear that, like the region’s secular dictators, Morsi might use the security police against his opponents as a tool of political power.

"They are trying to build a new regime exactly like the old one, with all its disadvantages," said Mokbel, an artist with a small and slender frame who, between battles, studies painting in a graduate program in one of Egypt’s top art schools.

The protesters, Mokbel argued, are the ones defending the rule of law, standing up for their right to peaceful expression. With no personal gain, he said, they risk their lives for their cause, for one another and for their many friends who have fallen.

"We owe them something," he said. "Not just a better economic situation, a government that deals with the people, that is not authoritarian or repressive."

Mokbel might be among the more articulate protesters. In the on-again, off-again battles with the riot police near Tahrir Square, the combatants are usually teenagers or even children who appear to live much of the time in the streets. Many seem animated by the sport of it and ill-informed about the politics.

But Mokbel, part of an older network of activists that is the backbone of the protests, praised the street children for their energy.

"The street kids are the ones who have suffered the most at the hands of the police, and their demands are much lower — some dignity, respect from the police, a little better life economically," he said. "They are just releasing their anger."

Although he acknowledged that some among the demonstrators inevitably provoke the riot police with stones or gas bombs, he nonetheless argued that police aggression caused all the fighting.

"Police attacking protesters is what causes the chaos," he said.

While a few police officers in other cities have been killed by gunfire, the protesters in Cairo have never been armed. Unlike the bullets and batons of the riot police, Mokbel argued, the protesters’ rock-throwing was mostly harmless against their opponents’ armor, helmets and shields.

"Even from the Molotov cocktails, not a single police officer has died," Mokbel said. "We do not want to burn down a place that we will end up paying to rebuild."

Mokbel is the son of a government employee and grew up in a middle-class family. Like many unmarried Egyptians, he still lives with his parents here. And before the revolution, he said, he and his family dismissed politics as hopeless.

These days it keeps him up at night. He sometimes has trouble falling asleep because he is constantly checking his iPhone for Twitter updates or text messages from protesters who might need his help in some new skirmish with the riot police.

At any clash, he said, he knows he will find friends.

"There are a lot of really strong relationships, friendships," Mokbel said. "We have slept in the same places, been through the same things, been in a lot of crisis situations together."

Like many on the ground, Mokbel was briskly dismissive of the elite political opposition.

"It does not represent the opinion of the street," he said. Anyone who starts talking to the media on behalf of the revolutionaries has left them, he said.

And also like many others, Mokbel said he did not object to the Islamist ideology of Morsi or the Muslim Brotherhood. When Morsi and his Brotherhood allies won control of Parliament and then the presidency, Mokbel expected that, as former victims of the security forces, they would soon move to reform them.

But now the Islamists’ apparent monopoly on power has turned activists cynical about Egypt’s young democratic process. Since Morsi’s decree temporarily suspending the power of the courts to challenge his decisions, violence around the country has escalated sharply.

"When the regime smashes the judiciary against the wall and uses the police as a tool of repression, who will conduct elections?" Mokbel asked. "If we wait for elections, what guarantees do we have?"

Senior Brotherhood officials close to Morsi say moving too fast to reform the Interior Ministry might provoke an open revolt by the police at a time when public security is already fraying. Instead, after recent clashes with police officers killed dozens of civilians, Morsi publicly thanked the security forces for their work and in certain cities expanded police powers.

"We want to see at least a beginning of justice," he said.

And so last Friday Mokbel once again packed his gas mask and protective gloves into a shoulder bag, and he headed out into the street for the inevitable fight.

First he joined a march to the palace, to help protect the protesters from a rumored Islamist ambush. Then he raced downtown to clashes along the Nile, but they quickly petered out.

Finally, as he was resting his legs just after sunset in a bohemian cafe, a handful of provocateurs among the mostly peaceful crowd outside the palace hurled gas bombs over its walls, setting fire to a gatehouse.

The police responded, as usual, with tear gas and, eventually, birdshot.

"Of course the police have the right to defend the palace," Mokbel said, heading into the fight. "But the tear gas doesn’t just target the people who threw the gas bombs. It is against the whole crowd."

"A lot of tear gas," he said, smiling wanly after about two hours of racing through the smoke to try to throw back the canisters. "So there is enough for everyone."

© 2013 The New York Times Company