WASHINGTON (CNN) -- President Bush heads to Japan on Saturday for his final G-8 summit of world leaders as the global economy slumps, energy prices soar and food shortages loom in the developing world.

Bush says he will press other leaders of the Group of Eight industrialized nations to follow through on their commitments from earlier summits, but has warned there is nothing he or anyone else can do in the short term about oil prices.

"It took us a while to get into the energy situation we're in and it's going to take us a while to get out of it," he said Wednesday in an appearance at the Rose Garden to preview his trip.

He continued to advocate more drilling in protected areas of the U.S. as a medium-term fix for skyrocketing fuel costs.

"Ultimately, of course, we're going to transition away from hydrocarbon. But we're now just in a transitional period and we need more oil to be able to do so," he said. Watch what may be in store for the world economy »

Bush's main economic goal at the summit in Toyako, on Japan's northern Hokkaido island, may be defensive, said CNN analyst David Gergen, former adviser to Presidents Nixon, Ford, Reagan and Clinton. Watch what's at stake at the summit »

"What's essential in this summit for George W. Bush is to make sure the world economy does not spin downward," he said.

Yet Bush is not raising expectations about what he and the other G-8 leaders can realistically accomplish on the economic front.

"One thing we need to make clear when I'm with our partners is that we're not going to become protectionists, that we believe in free trade and open markets," he said Wednesday.

A former administration official who served on the National Security Council under Bush says the G-8's purpose is not to come up with quick solutions.

"This is not a meeting of heads of state that leads to a treaty. It's really kind of public opinion shaping and trying to get people to agree that issues are important," said Michael Green, now with the Center for Strategic and International Studies. Watch how protesters are anticipating the summit »

At the summit, Bush, mindful of his legacy, also plans to press G-8 countries to keep their past financial commitments of aid to the developing world.

"G-8 countries have made pledges to help developing nations address challenges, from health care to education to corruption. Now we need to show the world that the G-8 can be accountable for its promises and deliver results," he said Wednesday.

Still, even as he presses other nations to write checks to back up their pledges, Bush is having trouble persuading U.S. lawmakers to do the same.

Congress has not yet authorized funding to continue the president's emergency plan for HIV/AIDS relief, a program that supplies HIV medicine to roughly 1.5 million people worldwide and is widely considered a foreign policy success for the Bush administration.

Bush arrives in Japan on Sunday, his 62nd birthday, and will meet Japan's prime minister, Yasuo Fukuda.

In addition to meeting among themselves, the G-8 leaders will be joined Monday by leaders from seven African countries: Algeria, Ethiopia, Ghana, Nigeria, South Africa, Tanzania and Senegal.

On Wednesday they will meet the leaders of Brazil, China, India, Mexico and South Africa.

Bush will have bilateral meetings with South Korea's President Lee Myung-bak and China's President Hu Jintao on Wednesday, in preparation for his visits to their countries next month.