CAIRO – Osama bin Laden appeared for the first time in three years in a video today released ahead of the sixth anniversary of the September 11, 2001 attacks, telling Americans they should convert to Islam if they want the war in Iraq to end.

The 30-minute video was obtained by the SITE Institute, a Washington-based group that monitors terror messages. American officials said the American government had obtained a copy earlier and intelligence agencies were studying the video to determine whether it was authentic.

In the video, which was broadcast to the Arab world by Al-Jazeera television, Mr. bin Laden sits as he talks, wearing a white robe and turban and beige cloak seated behind a table while reading an address to the American people from papers in front of him.

His trimmed beard is shorter than in his last video, in 2004, and is fully black — apparently dyed, since in past videos it was mostly gray. He speaks softly, as he usually does, and has dark bags under his eyes but appears healthy.

The footage gives a rare look at the Al Qaeda leader, who has likely avoided appearing in videos as a security measure. His emergence comes at a time when terrorism experts believe his terror network is regrouping in the lawless Pakistan-Afghanistan border region.

Mr. bin Laden makes no overt threats and does not directly call for attacks, according to the transcript, which was first posted on ABC’s Web site. Instead, he addresses Americans, lecturing them on the failures of their leaders to stop the war in Iraq despite growing public opposition in America.

“There are two solutions to stopping it. One is from our side, and it is to escalate the fighting and killing against you. This is our duty, and our brothers are carrying it out,” Mr. bin Laden said.

“The second solution is from your side,” he said. “I invite you to embrace Islam.”

“It will also achieve your desire to stop the war as a consequence, because as soon as the warmongering owners of the major corporations realize that you have lost confidence in your democratic system and have begun to look for an alternative, and this alternative is Islam, they will run after you to please you and achieve what you want to steer you away from Islam,” he said.

He derides President Bush, saying the American leader is backing Shiites against Sunnis in Iraq. But, bin Laden said, events in Iraq have gotten “out of control” and Mr. Bush is “like the one who plows and sows the sea: He harvests nothing but failure.”

Mr. bin Laden said the prestige of mujahedeen — Islamic holy warriors — has “grown globally” while America has been “bled dry economically.” The video appeared to have been recently made, since bin Laden refers to the Democratic Party’s congressional victory in last fall’s election and the President of France, Nicholas Sarkozy, who was elected in May.

The transcript also praises the American political activist and author Noam Chomsky, mentions global warming and refers to the Aug. 6 anniversary of the atomic bombing of Hiroshima during World War II.

Al Qaeda annually uses the anniversary of the Sept. 11 suicide attacks on the World Trade Center and the Pentagon as a propaganda opportunity, issuing videotapes to rally supporters and mock America.

But the appearance of Mr. bin Laden this year makes a bigger splash. The Al Qaeda had not appeared in new video footage since October 2004, and he had not put out an audiotape in more than a year, his longest period without a message.

A terrorism expert at the RAND think tank, Seth Jones, said that while the anniversary gives the pretext for the tape, it also comes at a time when the main Al Qaeda leadership has managed to regroup.

“There clearly has been a resurgence of core Al Qaeda in the tribal areas of Pakistan” along the frontier with Afghanistan since 2005, Mr. Jones said.

He said sympathy in that region for the Taliban has made it “more conducive to militant Sunni groups, including Al Qaeda.”

“It’s really created a sanctuary,” Mr. Jones said.

Director of the SITE Institute, Rita Katz, said she believes “strongly that Al Qaeda has regrouped” but that their headquarters are more diffuse than they used to be, comprising several training camps in Pakistan and Afghanistan.

She said it was likely that bin Laden is hidden in a more secure location, away from any of those sites.

America intercepted the video before it was released on Islamic Web sites where Al Qaeda usually posts its messages, an American counterterrorism official said in Washington. American officials had analyzed the video for hours before transcripts and videos were leaked, the official said, speaking on condition of anonymity because of the sensitivity of the issue.

The official said analysts were studying Mr. bin Laden’s physical characteristics — for clues about his health after unconfirmed rumors earlier this year that he had died of kidney disease.

White House deputy press secretary Tony Fratto declined to comment on the video until it had been fully analyzed, except to say it was a reminder of the continuing terrorist threat.

“This is why we need to be more vigilant and more persistent in our pursuit of terrorists,” Mr, Fratto said. “We will continue to pursue them. And it reminds us that we need to be certain that our intelligence professionals have all the tools they need to continue to disrupt their activities.”

The Homeland Security Department said it had no credible information warning of an imminent threat to America.

Soon after word emerged that Americas had the video, Islamic militant Web sites that usually carry statements from Al Qaeda went down and were inaccessible. The reason for the shutdown was not immediately known.

A terrorism expert at globalterroralert.com, Evan H. Kohlmann, said he suspected it was the work of Al Qaeda itself, trying to find how the video leaked to American officials.

“For them this is totally disruptive that the U.S. government could have a copy before their targeted audience does,” he said. “They could be concerned and trying to plug the leak quickly.”