U.S. investigators are testing some suspicious-looking canisters found at former Al Qaeda sites in Afghanistan, but officials have tentatively concluded the group could not make chemical, biological or radiological weapons.

Searches of more than 40 sites used by Usama bin Laden's terrorist network yielded documents, diagrams and material that showed "an appetite for weapons of mass destruction," Defense Secretary Donald H. Rumsfeld said Wednesday.

Of 50 suspected Al Qaeda sites identified so far, 45 have been thoroughly examined, officials said.

"In terms of having hard evidence of actual possession of weapons of mass destruction, I do not have that at this stage," Rumsfeld told a Pentagon news conference.

Rumsfeld added that he had been shown photographs of canisters recently found at a former Al Qaeda site which could contain chemical agents. Their contents have yet to be examined, he said.

"Externally they appear to be weapons of mass destruction," he said. Asked to explain, he said, "They've got stuff on them that make reasonable people think there's something not good in there, and we're going to check them out."

Other officials, speaking on condition of anonymity, said the canisters are no more than six inches high and bear Cyrillic markings indicating they might be of Russian origin.

These officials said the canisters were probably harmless. They said Al Qaeda is known to have made a number of transactions in the past for useless items dressed up as chemical or other terror weapons.

Rumsfeld did not offer his own assessment of how far Al Qaeda had progressed toward developing weapons of mass destruction. Other officials with access to intelligence information on the subject said the terrorists had great ambitions but were in the earliest stage of pursuing them.

One official said the materials and equipment found in Afghanistan were so basic as to resemble items an ordinary American high school chemistry class would use.

Rumsfeld has said that while the Sept. 11 airplane hijackings that killed thousands was a stunning tragedy, terrorist groups with access to chemical, biological or nuclear weapons could wreak far greater havoc unless global terrorism is extinguished.

That is one reason the Pentagon has placed a high priority on searching former Al Qaeda camps and hide-outs in Afghanistan and interrogating captured Al Qaeda members for indications of other planned attacks and the group's links to countries that possess chemical, biological or nuclear weapons.

The searches also are designed to find clues to the whereabouts of bin Laden and deposed Taliban leader Mullah Mohammed Omar. Rumsfeld disputed the notion that both have vanished.

"We still believe they're in the country," he said. "We're still working on that basis, although we are looking some other places as well, from time to time."

The prisoner interrogations in Afghanistan are continuing. Gen. Richard Myers, chairman of the Joint Chiefs of Staff, said 90 Pakistanis among them will be sent back to their home country.

"We've screened these individuals and determined that they should be returned to their own government for disposition," he said.

Thirty al-Qaida and Taliban prisoners arrived Wednesday at the U.S. naval base in Guantanamo Bay, Cuba, from Afghanistan. They were the third group of prisoners to be flown to Guantanamo, where they will be detained and interrogated.

Eighty prisoners are now at the base in Cuba. Rumsfeld said interrogations there had not yet begun.

John Walker Lindh, the American Taliban fighter captured in Afghanistan in November, was still aboard the USS Bataan in the Arabian Sea on Wednesday. Rumsfeld said he would been transferred soon to Justice Department custody. On Tuesday Lindh was charged in federal court with conspiracy to kill U.S. citizens and providing support to terrorist organizations.

Asked about the expanding commitment of U.S. troops around the world -- most recently the arrival of troops in the Philippines to train anti-terror forces -- Rumsfeld said it was a challenge that must be met.

"If we have to go into 15 more countries we ought to do it to deal with the problem of terrorism, so we don't allow this problem to damage and kill tens and thousands more people," he said.

In Afghanistan, however, the Bush administration is steering clear of committing military forces to the British-led international stabilization force now present in Kabul.

President Bush told reporters at the White House that there are plenty of other countries willing to perform that mission.