WASHINGTON — American intelligence agencies are expecting Osama bin Laden to issue a triumphant message to Al Qaeda followers on the sixth anniversary of the September 11, 2001, terrorist attacks boasting of Al Qaeda’s growing numbers and success in the Middle East and Southeast Asia.

Yesterday, hundreds of jihadist Web sites announced the upcoming appearance by Mr. bin Laden with the tell-tale banner of al-Sahab, the Al Qaeda company that produces the organization’s increasingly professional propaganda videos. The upcoming video appearance for the mastermind of the September 11 attacks — his first live video address since the last week of the 2004 presidential contest — confirms the American intelligence community’s assessment that he is still alive. Mr. bin Laden’s last audio address was in July 2006. In the new video his beard is dark, evidence that he is using hair dye, according to one intelligence analyst. In prior appearances Mr. bin Laden’s beard is white and gray. The expected video message comes not only on the anniversary of September 11, but at a period when intelligence analysts have said intelligence about terrorists threats is equal to that of the summer before those attacks on the World Trade Center and the Pentagon. Since British authorities thwarted an Al Qaeda plot involving doctors and medical students in London and Glasgow in early July, new information has come to light suggesting Al Qaeda may have operational cells in America.

The New York Sun reported August 6 that some of the British plotters used secure e-mail chains to communicate with handlers in Germany that also contained email addresses believed to belong to operatives in America. One reason why congressional Democrats before the August recess agreed to a temporary bill granting the National Security Agency the authority to intercept communications between foreign and domestic suspects was the director of national intelligence’s publicly stated concerns about Al Qaeda’s increased operational capability.

Intelligence officials contacted yesterday by The New York Sun did not say Mr. bin Laden’s September 11 message was a signal for any attacks. “We are expecting general criticism of American foreign policy, a triumphal kind of tone, something like U.S. strategy has failed, look how much stronger al Qaeda is today,” an analyst who requested anonymity said.

Part of the message from Al Qaeda’s leader will likely be to announce new terrorist group mergers. It is customary at the end of video messages from their senior leaders to mention a series of organizations and struggles with whom they have affinity. Last year, Gemaa Islamiya, the Egyptian spin-off of the Muslim Brotherhood formerly led by Al Qaeda’s no. 2, Ayman Zawahiri announced that it was merging with Al Qaeda. Two likely candidates that may be announced in Tuesday’s video are Pakistani jihadist groups, Jaish e Mohammed and Lakhdar e Jhangvi.

Intra-jihadist cooperation is also evident in the recent Al Qaeda plots broken up in Germany and Denmark. as well as the model of Al Qaeda in Iraq’s Mujahadin Shura Council, which includes representatives of other like-minded terrorists such as Ansar al Sunna.

American officials are also expecting Mr. bin Laden to taunt President Bush as Mr. Zawahiri did in his video following the suicide bomb attacks at the Iraqi parliament. He asked Mr. Bush to meet him for a juice at the building’s cafeteria, the site of the bombing. “Part of this video will be to buck up the troops, part of this is aimed at the American public,” the American intelligence analyst said.