Amid blustery winds and driving rain, Defense Secretary Leon E. Panetta toured the 9/11 Memorial in New York on Tuesday, five days ahead of its formal dedication.

Panetta peered into the 30-foot waterfalls that mark the footprints of the World Trade Center towers that were felled in the 2001 terrorist attacks. The Pentagon chief then paused by a Callery pear tree that was pulled from the rubble in the days after the attack. The tree was taken to a nursery in the Bronx and was replanted late last year at the memorial site.

Panetta is the first Cabinet-level official from the Obama administration to visit the completed memorial, and his low-key trip kicked off a week that will probably be dominated by the 10th anniversary of the attacks. On Sunday, President Obama and the first lady will attend a ceremony dedicating the memorial.

The Pentagon chief, who previously led the CIA, said that the main terrorist threat to the United States now comes from places such as Yemen, Somalia and North Africa, where al-Qaeda offshoots continue to plan attacks on the United States. “There is no question that Yemen has risen to the top of the list,” Panetta said.

Previously, senior Pentagon officials had described Pakistan’s border region with Afghanistan as the nexus for planning U.S. attacks.

Panetta also described progress that the United States has made over the past several years in killing leaders of the terrorist group. “Of the top four al-Qaeda leaders . . . three are dead,” he told reporters.

On Monday, Pakistani military officials said that their top spy agency had worked with the CIA to arrest Younis al-Mauritani, an al-Qaeda militant leader. The arrest is noteworthy because it suggests that the recently rocky relationship between the two countries is improving. “We have continued to urge the Pakistanis particularly to work with us in going after some key terrorist targets, and this is an indication that they are cooperating with us,” Panetta said. “It is a good sign.”

Panetta also used the New York visit to recall his own memories of Sept. 11, 2001. When the terrorists attacked, Panetta was on Capitol Hill testifying on ocean issues. One of his fellow panelists, who had an office in New York, leaned over and told him about the attacks. Panetta relayed the word to lawmakers, who canceled the remainder of the session.

He was stuck in Washington for several days before he was able to rent a car and drive to California, where he lives. The cross-country trek proved felicitous. “It gave me a chance to see how the rest of the country came together, driving through the Midwest and seeing signs up saying ‘God bless America,’ ” he said.

Panetta was accompanied to New York on Tuesday by five service members who joined the military after the attacks and who have served in Afghanistan, Iraq and Haiti. In recent weeks, the Obama administration has begun to refer to such Americans as the “9/11 generation,” a moniker intended to echo World War II’s “greatest generation.”

Panetta spent about 30 minutes touring the memorial with New York Mayor Michael R. Bloomberg (I). As they gazed at the waterfalls from underneath umbrellas, heavy wind whipped the water, which spills into black granite pools.

Panetta also planned to visit the memorial in Shanksville, Pa., to those killed on United Airlines Flight 93. But high winds prevented his V-22 Osprey, which takes off like a helicopter and flies like a plane, from landing at the airport nearby.

Panetta rarely uses the costly V-22s for domestic travel. The Ospreys, which can fly farther and faster than conventional military helicopters, have been put into heavy use in Iraq and Afghanistan. On Tuesday afternoon, the V-22 took him from Dover Air Force Base, where he had spent Monday night, to the Wall Street district. He had spent the night at Dover because his flight from California could not land in Washington. He spends many weekends at his home in California’s Carmel Valley.

Panetta was struck with the V-22 after his maiden voyage. “How did you like that gizmo?” he asked reporters as they left New York for the Pentagon’s helicopter pad.