National Security Adviser Condoleezza Rice said Thursday that the White House is concerned that Usama bin Laden's fractured Al Qaeda terror network could be regenerating in havens across the globe.

In a disturbing correlation to her remarks a 30-year-old, Saudi-born Palestinian is emerging as bin Laden's third-in-command, and U.S. officials believe he is actively organizing Al Qaeda cells to commit new acts of terror against Americans.

U.S. officials said Thursday that they have assumed for some time that Abu Zubaydah has assumed Al Qaeda's operational responsibilities following the death of Muhammad Atef, the terror organization's former chief of operations, who was killed by an American bomb in November.

Rice, President Bush's top foreign policy adviser, told The Associated Press that the United States continues to aggressively pursue bin Laden because "we assume he's alive," even as his Al Qaeda network operates without its former command structure.

She said U.S. officials are at a loss to judge how dangerous the remnants of Al Qaeda could be. "It's a little hard to know what effect just breaking all that up is having," Rice said.

Zubaydah has a thorough knowledge of Al Qaeda's entire worldwide network, much of which he recruited.

Officials said Zubaydah, whose full name is Zayn al-Abidin Muhammad Husayn Abu Zubaydah, is believed to have been in Afghanistan or Pakistan last fall, but his current whereabouts are unknown.

He is an expert at moving around the world undetected and has frequently served as the only direct link between senior Al Qaeda members and the organization's terrorist cells around the world.

According to a report in Thursday's New York Times, Zubaydah has been linked directly to the planning of the Sept. 11 attacks on the World Trade Center and the Pentagon, as well as a wave of attacks that were planned to occur in Europe last year — including plots to bomb the U.S. embassies in Paris and Sarajevo, Bosnia-Herzegovina.

"He's as dangerous as anyone we are looking for, including bin Laden," a senior law enforcement official told The Times.

Zubaydah, who has been one of bin Laden's top men for several years, uses multiple passports and aliases and has taken great care to avoid being photographed, the Times reported. One publicly available photograph is grainy and indistinct; U.S. intelligence agencies are believed to have more recent images.

Tall, light-complexioned and able to speak at least some English, Zubaydah has managed to move continuously around the world undetected even as other Al Qaeda officials outside of Afghanistan or Pakistan were captured in the years following the 1998 bombings of the U.S. embassies in Kenya and Tanzania.

Despite his prominence, Zubaydah has been so elusive that American law-enforcement officials have been unable to make any public charges against him, and he was left off both the Most Wanted list put out by the FBI in October and the list of potential terrorists issued by Attorney General John Ashcroft on Monday.

Born in Riyadh, Saudi Arabia, to a wealthy family in the Palestinian diaspora, Zubaydah did not become involved with militancy of any kind until his 20s, when he met bin Laden.

"He's interesting for many reasons," The Times quoted a Bush administration official as saying, "including the fact that he bypassed the more typical, nationalist route that leads other Palestinians into terrorism.

"His central goal has never been a Palestinian state," the official continued. "It's been the cause of Islamic extremism."

For a large part of the past decade, Zubaydah operated out of Peshawar, Pakistan, supervising the thousands of young volunteers from around the Muslim world who came to train with Al Qaeda in Afghanistan.

Zubaydah would screen them in the Al Qaeda compound in Peshawar, known as the "House of Martyrs," and also ran one of the training camps in Afghanistan himself.

Even more significantly, it was Zubaydah who would meet the freshly trained recruits upon their return from Afghanistan — and who would then assign each one to Al Qaeda cells around the world.

American officials believe Zubaydah is one of the few men alive who knows the names and missions of virtually all Al Qaeda operatives outside of Afghanistan or Pakistan.

Zubaydah first drew notice from terrorism analysts when information was received showing that he had masterminded the foiled "millennium plots" to attack Los Angeles International Airport and tourist areas in Jordan on New Year's Eve. He has been subsequently sentenced to death in absentia in Jordan.

Ahmed Ressam, the Algerian whose arrest in December 1999 helped uncover the millennium plots, testified at an accomplice's trial in July 2001 that Zubaydah had received him as an Al Qaeda recruit in Peshawar in 1998.

"He is the person in charge of the camps," Ressam testified. "He receives young men from all countries. He accepts you or rejects you. And he takes care of the expenses of the camps. He made arrangements for you when you travel, coming in or leaving."

Since Sept. 11 and the death of Atef in November, Zubaydah has apparently risen to be the No. 3 man in Al Qaeda, third only to bin Laden and Ayman al-Zawahiri, the Egyptian physician who merged his own organization with Al Qaeda in 1998.

Zubaydah's satellite phone number was found programmed into the memory of a cell phone used by a man thought to be the ringleader of the plot to blow up the American Embassy in Sarajevo. The confession of one of the men in the Paris embassy bomb plot, which operated out of Brussels, Belgium, linked him to that planned attack as well.

The Associated Press contributed to this report.