Usama bin Laden's voice sounded tired in an audiotape released Friday and, once again, he conspicuously avoided showing his face.

The 19-minute tape was the latest in a string of messages from the Al Qaeda leader this year that have been strong on propaganda, but have said little about how the terror network will continue its "jihad" against the United States — raising questions about bin Laden's level of control.

Bin Laden has not appeared in a video since October 2004 and did not issue any messages in 2005. This year, he has made four audiotapes, part of a stepped-up media campaign by him and his top deputy, Ayman al-Zawahiri, who has appeared in several videos.

But terror experts said the Al Qaeda leader's reluctance to appear on video probably does not indicate he is in poor health and instead is likely a security measure, to prevent hints of his location from slipping out.

Bruce Hoffman, a RAND counterterrorism expert based in Washington, said it may also be that bin Laden is trying to increase the drama of an eventual appearance.

"You do videotape when there's something important," Hoffman said. "When bin Laden appears it's something very special. He's as shrewd a showman as they come, and his sense of choreography is very high."

So far, the opportunity hasn't presented itself, a sign the Al Qaeda leader — believed to be hiding in the Afghan-Pakistan border region — is seeking for now just to show he survives and remains in control.

"What do you have to brag or crow about if you're sitting in a cave trying to avoid capture," Hoffman said. "So he's trying to leverage off of events to show his presence."

U.S. intelligence officials believe the voice on the audiotape is bin Laden, said a counterterrorism official who spoke on the condition of anonymity.

In the message, bin Laden paid tribute to the slain Abu Musab al-Zarqawi, seeking to show the Islamic militant was his follower.

Al Qaeda advertised Friday's message prominently on Islamic Web forums more than 24 hours before it was posted — suggesting the importance of the tribute to al-Zarqawi, the leader of Al Qaeda in Iraq who often appeared more of a rival than a follower.

The Jordanian-born al-Zarqawi, who was killed in a June 7 U.S. airstrike, became a hero among extremists by positioning himself as Al Qaeda's leading militant in Iraq.

In the audiotape, bin Laden praised al-Zarqawi in rhymed couplets traditional to Islamic poetry, calling him a "lion of Islam" who was "not just an honor to his tribe, his country and his Islamic nation, but to all mankind."

The audiotape narration accompanied a video showing old footage of al-Zarqawi, in a split screen with an old photo of bin Laden.

Bin Laden's voice — always quiet in his messages — sounded fatigued in the audio. He demanded President Bush release al-Zarqawi's body to his family and that Jordan allow him to be buried in his homeland, something Amman has said will never happen.

Al Qaeda's central leadership is believed to have differed with al-Zarqawi, criticizing his strategy of targeting Shiite civilians with suicide bombings in an attempt to spark a civil war in Iraq.

Bin Laden defended al-Zarqawi in the audiotape, saying he had "clear instructions" to focus on U.S.-led forces in Iraq but also was free to mount attacks on anyone who sided with the U.S.-led coalition "regardless of their sect or tribe."

However, bin Laden did not mention Shiites Muslims in particular, underlining the divisions with al-Zarqawi, who frequently railed against Shiites.

The Al Qaeda leader — perhaps inadvertently — also showed a lack of a direct hand in the fight in Iraq, said Diaa Rashwan, an Egyptian expert on militant groups.

In particular, bin Laden made no mention of al-Zarqawi's successor, or even the name of al-Zarqawi's organization, Al Qaeda in Iraq, Rashwan noted.

Instead, bin Laden said, "The banner has not fallen, it has only been passed from one lion to another."

"He doesn't appear to even know al-Zarqawi's successor," Rashwan said. Al Qaeda in Iraq has named a little-known militant as its new leader, with the pseudonym of Abu Hamza al-Muhajer.

Bin Laden also addressed Bush, saying, "We will continue to fight you and your allies everywhere, in Iraq, Afghanistan, Somalia and Sudan to run down your resources and kill your men until you return defeated to your nation."

But like other tapes this year, there was little sign of the direction of bin Laden's fight.

He issued a message in January warning his followers were planning a new attack in the United States. But his other three since then have been more focused on current events, including U.N. plans for a peacekeeping force in Sudan. He issued a message saying Zacarias Moussaoui, just convicted in the United States, had nothing to do with the Sept. 11 suicide hijackings.

"I think he's conscious that while he's been doing all the talking, al-Zarqawi has been doing all the fighting," Hoffman said.