Aso, who is struggling to stay in power, was the first foreign leader to visit the Obama White House, and the U.S. president called the prestigious invitation "a testimony to the strong partnership between the United States and Japan."
"The friendship between the United States and Japan is extraordinarily important to our country," Obama told reporters. "We think that we have an opportunity to work together, not only on issues related to the Pacific Rim but throughout the world."
The Japanese leader, sitting next to Obama in the Oval Office before their private meeting, said the world's first and second largest economies "will have to work together hand in hand" to solve the "very critical, vital" issues of the world.
Aso, of late, has faced single-digit approval ratings, appeals from his own party to resign and the worst Japanese recession in 50 years.
His selection as the first foreign leader to meet with Obama, however, shows the new U.S. administration is interested less in giving Aso a boost than in sending a message - to Tokyo and to the world - that Japan, a sometimes-neglected ally, remains an important partner in addressing global economic and security crises.
Japan trails only China as the largest foreign holder of U.S. Treasury bonds, holdings that help finance the ever-growing U.S. budget deficit. Japan also is the linchpin of U.S. security efforts in Asia, hosting about 50,000 U.S. military personnel and working with the United States and three other countries to press an increasingly hostile North Korea to give up its nuclear bombs.
Washington's invitation to Aso, who arrived Monday night for a 24-hour visit, was a broad signal "to the Japanese political establishment that the Obama administration is going to work with whoever is there," said Michael Auslin, a Japan specialist with the American Enterprise Institute think tank.
"If we continue to wait for the next Koizumi, the next strong leader, we're going to be waiting forever," Auslin said.
Since popular former Prime Minister Junichiro Koizumi left office in 2006, he has been followed by a series of ineffectual leaders.
Aso's administration reached a low point last week when his finance minister stepped down after appearing to be drunk during a world finance ministers' meeting.
Still, Secretary of State Hillary Rodham Clinton's response, when asked in Tokyo about the embarrassing resignation, signaled a U.S. willingness to stand by Japan regardless of political or economic turmoil: "I think that the resilience of the Japanese people and the Japanese government is what's important here."
Aso's visit, while symbolically important, might be overshadowed as Obama presses a series of politically sensitive economic initiatives; Aso came to Washington on the day of Obama's first address to a joint session of Congress.
Japan has been looking for U.S. reassurance about its place as the top U.S. ally in Asia. Some in Tokyo are worried about increasing U.S. cooperation with, and dependence on, China on a host of diplomatic, economic and military matters.
Clinton's decision to make Tokyo her first destination as secretary of state, as well as Aso's early White House visit, are important signals from the Obama administration. Japan still remembers that Clinton's husband, former President Bill Clinton, bypassed Tokyo during a trip to China in 1998.
"The sentiment in Japan is quite delicate right now in terms of what place it holds in U.S. priorities," said John Park, a senior researcher at the United States Institute of Peace.
Secretary of State Clinton has also sought to soothe Japanese anger over the Bush administration's handling of North Korea's abduction of Japanese citizens in the 1970s and '80s. The United States, despite vehement public and private Japanese protestations, removed North Korea last year from a U.S. terrorism blacklist, which Japan felt was one of the few levers negotiators had with the North on the abduction question.
Clinton met with the families of kidnapped Japanese during her visit to Tokyo and pledged to give the matter a high priority in stalled disarmament talks with North Korea.