By Mark Trevelyan, Security Correspondent

LONDON, Sep 21 (Reuters) A German-language mouthpiece for al Qaeda has re-emerged on the Internet, vowing to defy the authorities despite this month's arrest of suspects linked to it in Austria and Canada.

On sites easily traceable via search engines, the German-language arm of the ''Global Islamic Media Front'' (GIMF) appeals for volunteer translators, inviting them to reply to a Hotmail address, and posts links to dozens of al Qaeda videos.

''After some brothers and sisters were arrested (may Allah free them) and the Forum and blog of the GIMF were removed, we say this: the GIMF still exists and will continue its work,'' a statement from the front says.

''To the Kuffar (infidels) who try to fight us, we say: you can do what you like, make as many arrests as you like...you will not reach your goal. We will always keep going until we achieve victory or martyrdom.'' The re-emergence of the GIMF in German highlights the difficulty for authorities of shutting down radical Islamist Web sites, which often simply spring up at new addresses.

''This can be done in minutes. It can be automated. You will never catch it. Once you try to hit it, it's already at another destination, another point,'' said Harald Summa, chief executive of Eco, the association of German Internet enterprises.

No comment was available from the German prosecutor's office. But authorities in Germany, where three men were arrested earlier this month over an alleged plot to commit ''massive bomb attacks'', have expressed concern about the spread of al Qaeda propaganda in the German language.

In an unconnected operation a week after the German swoop, Austria arrested three people with alleged al Qaeda links who are suspected of posting a video last March threatening attacks against Germany and Austria.

One has since been freed but the other two suspects -- a married Austrian couple, both in their 20s and of Arab origin -- remain in custody. A man suspected of being in contact with them via email and online forums has been charged in Canada with plotting to cause explosions in a foreign country.

One of the new GIMF sites in German contains several online postings in response to its latest statement.

''Brothers, I would like to be in contact with you because I want to become a mujahideen (fighter) after I finish my studies, inshaallah (God willing),'' wrote one contributor, Ameen. It was impossible to say if the naive-looking comment was genuine.

Group of Eight (G8) countries vowed at a summit in Germany in June to work together to combat ''terrorist and criminal abuse'' of modern communications technology. European Union Justice and Security Commissioner Franco Frattini is due to present proposals next month to block access to Web sites that contain instructions for bomb-making.

REUTERS ARB HT1952