Updated

Usama bin Laden's call to arms to Muslims around the world, if authentic, would be a stark reminder that the Al Qaeda founder had eluded all U.S. efforts to kill or capture him, even with a $25 million price on his head, and probably still presides over a far-flung terror network.

Terrorism experts suggested that the taped message could signal a determination by bin Laden to re-emerge at this time to menace the United States and its allies. At the same time, some analysts pondered why the message was an audiotape rather than a videotape, as bin Laden has used in the past — and whether that suggested he was seriously ill or had changed his appearance.

U.S. intelligence experts said Wednesday they believed the broadcast voice was that of the Saudi exile believed to have masterminded the Sept. 11, 2001, terror attacks against the World Trade Center and the Pentagon. Government analysts continued tests to make sure the recorded voice was authentic and recent.

Experts said the taped message — in which the speaker praised last month's terrorist strikes in Bali and Moscow and warned U.S. allies to back away from plans to attack Iraq — could be the prelude to a new major terror attack. Broadcast on the Arabic-language TV station al-Jazeera in Qatar, the tape appears to be the clearest evidence yet that bin Laden survived the U.S.-led military assault, including extensive bombing of suspected hideouts in Tora Bora in eastern Afghanistan.

The failure to learn more solid information on bin Laden's fate has been a major source of frustration for the Bush administration — a frustration the new tape only increases. Shortly after the Sept. 11 attacks, Bush said he wanted bin Laden "dead or alive." More recently, Bush has sought to play down bin Laden's individual significance.

Larry Johnson, deputy chief of counterterrorism in the first Bush administration, said the tape suggests bin Laden's Al Qaeda operation remains in business "as a heretical branch of Islam combined with the criminal instincts of the Mafia. It also may signal another major attack coming up."

"I am struck by the fact that they did not release a videotape," Johnson added. He said that Al Qaeda might be planning to release a videotape once a new attack is carried out.

Other analysts suggested that audiotapes are easier to produce and smuggle out of a country than videotapes, that bin Laden might have changed his appearance, although that might be hard to do for the thin, over six-foot-tall fugitive, or that he might be gravely ill.

George Michael, an Arabic translator who analyzed a previous bin Laden tape for the Pentagon, said he was persuaded that it was indeed bin Laden, although he sounded "more tired and aged."

"There's a very faint beeping noise like it's coming from a medical machine," Michael added. "Perhaps his health condition is bad."

Little was known about the tape. Al-Jazeera's chief editor, Ibrahim Hilal, said the network's reporter in the Pakistani capital of Islamabad obtained it and played it over the phone for the station. The reporter, Ahmad Muaffaq Zaidan, said he got the cassette from a bin Laden emissary who wore a mask and refused to answer any questions.

Daniel Benjamin, a former terrorism expert on the Clinton administration's National Security Council, said that if the voice on the tape turns out to be bin Laden's, "then his sense of stagecraft remains superb."

"He picked a moment when the confrontation between the international community, led by the United States, and Iraq had reached a peak — and he is emerging once again as the champion of the Muslims, casting this as another step in America's war against Islam," said Benjamin, co-author of a new book on bin Laden, The Age of Sacred Terror.

"It is causing heartburn for the administration because there will be a lot of questions as to why we are focusing our attentions on Saddam Hussein at a time when a man who has more than 3,000 dead Americans on his account has resurfaced," Benjamin said.

Senate Intelligence Committee Chairman Bob Graham, D-Fla., suggested bin Laden's warning could suggest Al Qaeda had "an intact command and control capability," perhaps with chilling consequences for the United States, where it maintains "a significant number of operatives."

Even so, Sen Richard Lugar, R-Ind., incoming chairman of the Senate Foreign Relations Committee, said there's still a chance the tape is bogus. "Some [analysts] said he is talking too fast. Others have analyzed the content and wondered if this was not once again a clever ruse in which you bring up current events to show you are alive," Lugar said.

On the tape, the speaker also makes threats against Britain, France, Italy, Canada, Germany, Australia, Indonesia, Tunisia, Kuwait, Jordan, Russia, and Pakistan.