(AP) Now that Osama bin Laden has again placed himself in the public eye - or, at least, in the public ear - with a threatening audiotaped statement, U.S. counterterrorism officials wonder if he has taken on a new appearance.

Because he delivered his message via audio, rather than video, intelligence officials suggest the al Qaeda leader may have wanted to conceal his appearance.

Officials have only a suspicion, but no evidence, that his appearance may have changed since his last videotaped statements from roughly a year ago.

His whereabouts remain unknown. According to U.S. officials, America's best bet for his location has not changed: the wild mountains along the border of Afghanistan and Pakistan, a remote tribal region where U.S. and allied forces fear to go.

"I don't think we've ever said that we had any good evidence of where he is," Defense Department spokeswoman Victoria Clarke said recently.

The long and fruitless search was on the mind of Russian President Vladimir Putin during a news conference Friday with President Bush in Pushkin.

"Now, where has Osama bin Laden taken refuge? They say that somewhere between Afghanistan and Pakistan," he said.

The one-time Saudi aristocrat looked haggard and gaunt in one of his last videos, which was probably filmed in Afghanistan in late November or early December 2001.

Counterterrorism officials believe he was sensitive to the widespread reporting that described him as such, and may be trying to hide ailments and injuries from public view.

In fact, officials believe he may have been wounded in Tora Bora, his presumed hiding place in eastern Afghanistan around that time. Rumors persist that he suffers a kidney ailment, something U.S. intelligence officials have never verified.

Officials also speculate he has somehow disguised himself, but have no firm evidence.

Bin Laden is not above using misdirection to foil pursuit. Before the war in Afghanistan, he used look-alike decoys and fake caravans, and is believed to have moved around the country hidden in an ambulance.

The audiotape that pushed bin Laden back into the fore was aired Nov. 12 on al-Jazeera, an Arabic television network. Intelligence officials analyzed the message and said it was an authentic, unedited recording.

The statement read promised new terrorist attacks and made references to several recent events. The message is the first hard evidence in almost a year that bin Laden survived the U.S. onslaught in Afghanistan.

While the tape prompted new worries of an imminent attack, bin Laden's effort to make public statements may expose him to detection, even if he is holed up in the remote mountains of Pakistan and Afghanistan.

Despite Bush administration attempts to de-emphasize bin Laden himself as the focal point of the war on terror, many regard him as the key target to dismantle his network.

The capture this year of several top lieutenants of bin Laden has not provided U.S. intelligence officials with the specific information to find him.

Earlier in November, U.S. authorities took into custody bin Laden's Persian Gulf operations chief, Abd al-Rahim al-Nashiri. In June, they had Omar al-Farouq, bin Laden's top man in Southeast Asia, and operational chief Abu Zubair al-Haili. In March, they captured Abu Zubaydah, al-Qaida's top terrorism coordinator, in Pakistan.

But they either do not know or have managed to conceal bin Laden's whereabouts.

The area along the Pakistani-Afghan where bin Laden may be holed up is huge and a place where `there is not government authority on either side, and there's lots of places for him to hide," said Vince Cannistraro, a former CIA counterterrorism chief.

Other recent rumors, largely discounted by U.S. officials, have placed him in Pakistani cities, in Yemen or in Saudi Arabia.

Cannistraro said the only other place safe place for bin Laden is a tribal region along the border of Saudi Arabia and Yemen, where he has family connections. But he would have difficulty reaching there from Afghanistan without being detected.