Simply by showing up, President Barack Obama is making good on a promise — twice deferred — to visit Australia. It also will be an occasion to renew bonds with an exceptionally close U.S. ally and strengthen the two nations’ defense posture in the Pacific region.

Obama set out Tuesday from Hawaii bound for the Australian capital of Canberra. Crossing the international dateline on Air Force One, he was to arrive midafternoon local time Wednesday for a day and a half visit.

For Obama and Australia, the third time’s the charm. He canceled two earlier visits, once to stay in Washington to lobby for passage of his health care bill, and again in the wake of the oil spill in the Gulf of Mexico. 

The president is expected to announce that the U.S. is expanding its military presence in Australia, positioning U.S. equipment there, increasing access to bases, and conducting more joint exercises and training. 

The moves would counter an increasingly aggressive China, which claims dominion over vast areas of the Pacific that the U.S. considers international waters, and has alarmed smaller Asian neighbors by reigniting old territorial disputes, including confrontations over the South China Sea. Defense Secretary Leon Panetta has said that the goal is to signal that the U.S. and Australia will stick together in face of any threats. 

Deputy national security adviser Ben Rhodes, speaking with reporters on the flight to Australia, said that serving as a counterweight to China’s growing influence was just one factor in the ramped-up U.S. military presence in Australia.

Others included being able to respond more quickly to natural disasters in the region, such as the devastating earthquake and tsunami earlier this year in Japan, and fighting terrorism and piracy on the high seas to help keep sea lanes of commerce open.

An increased U.S. presence would help the United States “protect our interests, protect our allies” and help it “play its critical role as an anchor of stability and security in the region,” Rhodes said. 

Kim Beazley, Australia’s ambassador to the U.S., said the mere fact of Obama’s  appearance in the country was “enormously important” to Australians. And for the U.S., Australia’s geographic location in the burgeoning Asia-Pacific makes the longtime ally an increasingly important one as China’s might grows. 

“It’s an area where the United States has got considerable freedom of action, considerable interests, growing interests,” Beazley said in an interview. “And Australia is well-located strategically.” 

Arriving Wednesday afternoon, Obama is to meet with Prime Minister Julia Gillard, and the two will hold a joint news conference. On Thursday, Obama addresses the Australian Parliament before traveling to Darwin on Australia’s remote northern coast. 

It’s the first time a sitting U.S. president has been to Darwin, where U.S. and Australian forces were killed in a Japanese attack during World War II, and Obama will visit a memorial to the dead. Obama also will visit a military base in Darwin where he’ll speak to Australian troops and U.S. Marines. The visit comes as the U.S. and Australia mark 60 years as defense treaty partners. 

In a region of the world where volatility threatens, Obama’s visit is in large part about underscoring the tightness and steadiness of the relationship with an ally that has fought alongside the United States in nearly every conflict since World War I. 

He’s doing so in ways large and small, from promoting increased military ties between the two countries, to a planned visit with Gillard to a local school. A school visit was also part of the agenda when Gillard visited Obama at the White House in March. 

Obama will use his remarks in Australia to discuss the broad U.S. agenda in the Asia-Pacific, but while economics and trade have been the focus of the days he’s just spent in Hawaii hosting the Asia-Pacific Economic Cooperation summit, in Australia the focus shifts to security. 

Adm. Robert Willard, head of the U.S. Pacific Command, noted that the U.S. has a military presence in the South China Sea, but he said many of those forces are deployed from the West Coast of the United States or from Japan or South Korea, where the U.S. maintains bases. 

“Any opportunities that we have to locate forces in the Southeast Asia region relieves some pressure on that need to, at great expense, deploy and sustain forces,” Willard told reporters traveling with Obama in Honolulu on Sunday. 

“We have a very, very tight, close relationship with our Australian friends,” he said. 

Obama’s visit has been eagerly anticipated in Australia, where residents have generally been understanding about his previous cancellations. Obama’s predecessor, George W. Bush, was heckled when he spoke to the parliament in 2003, not long after the Australian government divided the nation by sending troops to support the invasion of Iraq. For a president facing poor poll numbers in the U.S. and the prospect of a difficult re-election campaign, the Australian audience may be as welcoming as any Obama could find at home. 

From Australia Obama will head to Indonesia for a security summit with Asian nations before finishing his nine-day trip and returning to Washington on Nov. 20.

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Associated Press writer Lolita C. Baldor in Washington contributed to this report.