Australia's new strategic alliance with the United States and United Kingdom is likely to see more troops, war planes and naval vessels in the Top End. But any expansion could be hindered by the controversial lease of Darwin Port to a Chinese company, national security experts say.

Heralded as the most significant shift in Australia's defence direction in decades, the centrepiece of the trilateral security partnership, dubbed "AUKUS", is a plan to build a fleet of nuclear-powered submarines.

But Defence Minister Peter Dutton has also flagged a major enhancement in Australia's military cooperation with the US, which currently deploys about 2,500 marines to the Top End each dry season.

John Coyne from the Australian Strategic Policy Institute said the 99-year lease of the Darwin Port to Landbridge could prove an impediment to the allies' military expansion plans.