A contingent of 200 US marines has arrived in Darwin in northern Australia, the first tranche of an eventual 2,500-strong rotating deployment.
It is part of President Barack Obama's plans to strengthen US capabilities in the Asia-Pacific region.
US and Australian leaders have stressed the deployment is not an attempt to contain China.
Australian leaders welcomed what they said was the latest chapter in a more than 60-year alliance with the US.
"It represents an evolution of existing exercises and activities that the United States already conducts with the Australian Defence Force in Australia," Prime Minister Julia Gillard, Defence Minister Stephen Smith and Northern Territory Chief Minister Paul Henderson said.
"The intent in the coming years is to establish a rotational presence of up to a 2,500 personnel Marine Air Ground Task Force, rotating into Northern Australia in the northern dry season.
"There are no (permanent) US military bases in Australia, and this will not change," they added.
The US military currently has only a limited deployment in long-standing ally Australia, including the Pine Gap Joint Defence Facility spy station near Alice Springs.
The latest move represents a significant geo-strategic shift by Washington and it has annoyed Beijing, whose rapid rise is reorienting Asia's balance.
China has said the Marines deployment is proof of a "Cold War mentality".
As part of the major expansion of military ties, Australia last week said it may allow the US to use its territory to operate long-range spy drones.
The US could also reportedly station aircraft carriers and nuclear-powered attack submarines in the western Australian city of Perth.
