RIYADH, Saudi Arabia >> In the Netherlands, the jailhouse recantations of a convicted terrorist renouncing violence have circulated online. Counterterrorism officials say they could make disaffected youth think twice about joining violent extremist ranks.

In Pakistan, the authorities are posting on YouTube gruesome videos of mosques bombed by Islamic extremists, to show that terrorist attacks mostly kill fellow Muslims.

And here in Saudi Arabia, a government-supported program has enlisted hundreds of Islamic scholars turned bloggers to fight online radicalization by challenging the interpretations of the Quran posted on extremist social networking forums.

In recent years, governments and allied grass-roots advocacy groups had largely ceded cyberspace to extremists, who use the Internet to recruit, raise money, spread their ideology and disseminate instructions on bomb-making and other terrorist techniques. Governments have carried out covert operations to undermine or take down extremist websites, but many sites pop back up again within days or weeks.

Now these governments, often working with international organizations like the United Nations and European Union, and more quietly with private or nonprofit groups, are trying to open a counterattack to undermine the appeal of terrorists, expose their lack of legitimacy, and attack the credibility of their ideology and online messengers.

Counterterrorism officials from more than 30 countries met here last week under the auspices of the United Nations in one of the largest gatherings of its kind, to share tactics and strategies on how to use the Internet to counter the appeal of extremist violence.

“The terrorist message, for all its deviancy and destructiveness, has gone unchallenged for too long,” said Richard Barrett, a conference organizer who heads a United Nations office that monitors sanctions on al-Qaida and the Taliban.

To be sure, many of these efforts to counter violent extremism on the Web are just getting off the ground. In some cases, small local initiatives are having success, and could find wider use on the global stage, but many others have foundered in what is a very fluid effort.

Officials measuring the campaigns acknowledge that finding the right messengers — from extremists who have renounced their violent pasts to Pakistani cricket stars who presumably have wide appeal among the youth who are being solicited by both sides — is as important as tailoring messages about the political, social and ideological issues that attract people to violent extremism.

There are signs that the new campaigns may be having at least a temporary impact. Evan F. Kohlmann, who tracks militant websites at the security consulting firm Flashpoint Global Partners, said a growing number of extremist forums are using password-protected sites to thwart hackers and dissenters.

Counterterrorism officials acknowledge they face an uphill challenge in coming up with an effective counter to al-Qaida’s simple but powerful narrative: that the United States and the West are at war with Islam; that Muslims are unjustly discriminated against and persecuted; and that only violent action can bring change.

Sidney Jones, an expert on Islamic terrorism at the International Crisis Group’s branch in Jakarta, said a 6,000-word critique of an Indonesian extremist group that was posted on several radical websites last March offered insights that could be used in broader counter-radicalization campaigns. The critique was disseminated shortly after the Indonesian counterterrorism police raided an extremist training camp in Aceh, in northern Sumatra.

“It argued that by running off to the jungle with guns and losing so many of its members, the movement was depleting its own resources and undermining its prospects for victory,” Jones wrote in a paper for the conference here.

Without credible messengers, however, even the most effective message will fall on deaf ears, especially in a growing number of campaigns to reach disaffected youth, counterterrorism experts say.

The U.S. government has struggled mightily in the years since the Sept. 11, 2001, attacks to develop an effective and credible campaign to counter the ideology and messages of al-Qaida and other extremist groups. The State Department is overhauling and expanding rapid-reaction teams meant to counter violent extremist messages throughout the world

Kohlmann of Flashpoint Global Partners said, “The problem is, you don’t have people in the U.S. government who are of the right generation to understand how social networking works, and at the same time who are knowledgeable enough about the Muslim world.”