The US Defence Secretary says he doubts Osama Bin Laden is in a position to command al-Qaeda's world operations.
Osama Bin Laden reportedly escaped capture in Afghanistan in 2001
Donald Rumsfeld told journalists en route to Pakistan that Bin Laden could be hiding somewhere on the Afghan-Pakistan border.
"I suspect...if he's alive and functioning, that he's probably spending a major fraction of his time trying to avoid getting caught."
He said the search for the Saudi-born militant would continue.
"I think it is interesting that we haven't heard from him for close to a year," Mr Rumsfeld said.
"I have trouble believing he is able to operate sufficiently to be in a position of major command over a worldwide al-Qaeda operation, but I could be wrong".
Last week, US ambassador to Pakistan Ryan C Crocker said he thought al-Qaeda was in serious trouble.
US officials have long argued that the war on terrorism has disrupted communications between the main al-Qaeda leadership and the rest of its scattered members.
Mr Rumsfeld also praised Pakistan's leader, General Pervez Musharraf, for his role in fighting al-Qaeda and other extremist groups.
He said it was "important that the world recognises the relationships the United States has had in the past with moderate Muslim states".
The BBC's Zaffar Abbas in Islamabad says Mr Rumsfeld's visit is aimed at ensuring continued US support in the relief and rehabilitation work in areas devastated by the recent earthquake.
Mr Rumsfeld said the US was pleased to be working side-by-side with President Musharraf and the Pakistani military to do whatever could be done to reduce the suffering of many Pakistanis.
Our correspondent says the US financial support and material support for the relief work has been one of the largest by any Western state.
Many believe that Washington has used the exercise to win support in an area where anti-American feelings run high.