"I have trouble believing that he is able to operate sufficiently to be in a position of major command over a world-wide al Qaeda operation but I could be wrong. We just don't know," Rumsfeld told reporters aboard his plane en route to Pakistan.
"I suspect that in any event if he is alive and functioning, that he is probably spending a major fraction of his time in trying to avoid being caught," he said.
"I think it is interesting that we have not heard from him for a year, close to a year. I don't know what it means."
"I think it is important that the world recognises the relationships the United States has had in the past with moderate Muslim states and what we do," he said.
Rumsfeld said the world should "see that the activities of the United States are to support those ... who are opposed to the people who cut off heads ... and engage in violent extremist activities."
He called Pakistan "a moderate Muslim regime in the world that is demonstrating ... partnership."
Bin Laden's whereabouts are unknown but speculation has focused on the rugged mountainous terrain along the border of Afghanistan and Pakistan.
Later Rumsfeld arrived in Islamabad for a first-hand look at areas that were devastated by the October 8 earthquake.
Rumsfeld, who arrived here unannounced, was received at Chaklala airbase Defence Minister Rao Sikandar Iqbal.
He later flew to Muzaffarabad and visited the main US MASH hospital.
He also visited a US surgical unit at Shinkiari in the NWFP, which has been treating the injured.
Rumsfeld also met pilots and crew of US Chinook helicopters at Qasim airbase in Rawalpindi, which have been shuttling the bulk of the relief supplies for millions of quake survivors.
On Tuesday US Vice President Dick Cheney held talks with President Pervez Musharraf and also visited quake-hit areas.
The United States has been one of the major contributors to the relief effort in Pakistan, a key ally in the US-led "war on terror."
Rumsfeld said there were currently around 850 US military personnel, 12 helicopters and two medical facilities set up to help the effort in Pakistan, where more than 73,000 people were killed.