Eman AbdelRahman is one of 200,000 people who have signed up on Facebook to back Mohamed ElBaradei, the former U.N. nuclear boss who has said he wants to shatter 30 years of political stasis in Egypt by running for president.

Despite a surge in online support for political alternatives to President Hosni Mubarak, 82, and who has been in power since 1981, even ardent supporters acknowledge that online activism in Egypt cannot deliver change without action on the streets.

We need collaboration from everyone in Egypt, including those who are online and those who are not -- students, workers, housewives, AbdelRahman, a 25-year-old engineer, said.

The speed supporters signed up to Facebook after ElBaradei returned to Egypt in February, adding tens of thousands in a few days, reflects pent-up frustration before parliament and presidential elections this year and next, analysts say.

But they say the challenge is galvanizing the masses in a country where opposition parties are weak, where police crush even modest protests and where the banned Muslim Brotherhood, the biggest opposition group, has shunned action on the streets.

It's unrealistic to think that online activism can turn things around without the existence of an opposition that can challenge the state, said political analyst Amr Hamzawy. There is a clear lack of constituency building on the ground.

Iran is cited as an example of how social networking tools can help rally hundreds of thousands. In the Islamic Republic, Twitter and other sites were used to draw protesters out against the 2009 presidential election result they said was rigged.

But opposition voices in Iran, even within confines set by the Islamic Republic's political system, are a more potent force than in Egypt where opposition parties are fragmented and have limited popular following.

MODEST PROTESTS

What bloggers did was expose the power of Iran's opposition ... Egypt does not have this grassroots audience, said Rabab el Mahdi, a professor at the American University of Cairo.

The Muslim Brotherhood, banned under a law that blocks any political group based on religion, is the only group in Egypt with a network across the nation that could, analysts say, bring tens of thousands onto the streets if it chose.

But the Brotherhood is wary of a confrontation that could bring a crushing security response, threatening the group's existence, analysts say. It has shunned street protests to focus on its medical and other social programs to build support.

Even modest protests in Egypt draw an overwhelming, and often violent, police response. But heavy-handed security has also been part of the reason activists have taken to the Web.

At one point the dynamism died down and activists found it difficult to mobilize in large numbers ... so they shifted to online gatherings, said blogger Hossam Hamalawy.

Facebook became a platform for rallying dissidents in 2008, after the April Sixth Youth movement drew over 70,000 supporters to its page to back a strike over surging food prices. Protests on April 6 of that year had led to clashes with police.

This year, on the anniversary of the 2008 protests, demonstrators turned out in Cairo chanting Down, down, Hosni Mubarak. Just a few hundred turned up, small by global standards but a rarity in Egypt. Heavily outnumbered by police, many protesters were beaten before the demonstration ended.

It has been a similar story at follow-up protests.

EMERGENCY LAW

Creating momentum may be a challenge for online activists in Egypt, a country of 78 million where the United Nations puts illiteracy at 34 percent and Internet penetration at 17 percent.

Iran, with a comparable population, has illiteracy of 18 percent while Internet usage of 31 percent.

Yet Egypt's government is still wary of the Web community.

The Internet is not policed as in Iran or some other Arab states where sites, including Facebook, are blocked. But bloggers and Web activists have been detained. Rights groups say Egypt has used a long-standing emergency law to do so.

In May, Cairo extended the law, already in place for almost three decades, for two more years, but said it would limit usage to terror and narcotics cases. Rights groups are skeptical.

Aware of the limits of the Web, some online ElBaradei supporters have gone offline by gathering signatures for a petition demanding constitutional changes and more freedom.

Yusuf AbdelRahman, representing ElBaradei's Facebook group, said the petition had 54,870 online signatures so far but added that 15,000 Facebook members have volunteered to go on the streets of Cairo and other cities to collect more signatures.

(This) is a crucial step considering that three decades of state repression has left many afraid of taking action. Others accept repressive measures as a fact of life, he said.

(Editing by Missy Ryan and Samia Nakhoul)