In Egypt, the tried-and-true tool for opponents of President Hosni Mubarak in recent years has been Facebook. Most recently, it was on Facebook - which boasts 5 million users in Egypt, the most in the Arab world - where youthful outrage over the killing of a prominent activist spread, leading to the protests in Cairo's Tahrir Square and Mubarak's promise to step down this year.

But Facebook, which celebrates its seventh birthday Friday and has more than a half-billion users worldwide, is not eagerly embracing its role as the insurrectionists' instrument of choice. Its strategy contrasts with rivals Google and Twitter, which actively helped opposition leaders communicate after the Egyptian government shut down Internet access.

The Silicon Valley giant, whether it likes it or not, has been thrust like never before into a sensitive global political moment that pits the company's need for an open Internet against concerns that autocratic regimes could limit use of the site or shut it down altogether.

"The movement [in Egypt] was very dependent on Facebook," said Alaa Abd El Fattah, an Egyptian blogger and activist in South Africa who has a strong following in Egypt. "It started with anger then turned into a legitimate uprising."

The recent unrest in Egypt and Tunisia is forcing Facebook officials to grapple with the prospect that other governments will grow more cautious of permitting the company to operate in their countries without restrictions or close monitoring, according to David Kirkpatrick, author of "The Facebook Effect," an authorized biography of the company's history. Facebook is also looking at whether it should allow activists to have a measure of anonymity on the site, he said.

"I have talked to people inside Facebook in the last week, and they are debating this internally," Kirkpatrick said. "Many countries where Facebook is popular have autocracies or dictatorships, and most of the countries have passively tolerated their popularity. But what's happened in Egypt or Tunisia is likely to change other countries' attitudes, and they'll be more wary of Facebook operating there."

A Facebook spokesman, Andrew Noyes, declined to make anyone at the company available to discuss its role in the Egypt protests or its strategy in politically fraught environments. In a short statement, Noyes said: "Although the turmoil in Egypt is a matter for the Egyptian people and their government to resolve, limiting Internet access for millions of people is a matter of concern for the global community. It is essential to communication and to commerce. No one should be denied access to the Internet."

(Washington Post Co. Chairman Donald E. Graham sits on Facebook's board.)

Even when Facebook has actively helped protesters work around government intrusions, the company casts its moves as mere technical solutions. Last month, after Tunisian security officials used a virus to secretly collect local Facebook user IDs and passwords, the Internet giant took action. It rerouted Tunisia's Facebook traffic to a site where local Internet service providers couldn't gobble up user information.

In a statement released to The Post, the company said it viewed the predicament as just a "security problem" in need of a fix.

"Certainly there's a political context to the particular circumstance in Tunisia, but from Facebook's perspective, what happened was a security problem that required a technological solution: we prevented an exploit that was making Facebook accounts vulnerable and restored the integrity of the compromised accounts," wrote Joe Sullivan, Facebook's chief security officer. "We would have taken the same approach in any situation where we saw a systematic exploit."

Yet Facebook seems to be veering in a different direction than Google, which has battled China over censorship, or Twitter, the microblogging site that earned renown during the Iranian protests of 2009 for delaying a scheduled shutdown and facilitating civil protest in Tehran. This week, Twitter, Google and SayNow, a voice-based social media platform, launched a service that provides Egyptians with phone numbers to call and leave messages, which are recorded and posted on the Internet. It's called Tweet2Speak.