A SECRET document that the government said did not exist and which outlines the rights, role and responsibilities of US forces in Australia is being kept from the public, due to concerns it would affect the relationship with America.

The document, classified ''Secret'' and signed in 2010 by the then US defence secretary, Robert Gates, and Australia's Defence Minister, Stephen Smith, is the only document created since 1963 that provides some official guidance for US troops in Australia.

Robert Gates (left) and Stephen Smith signed the document in 2010. Credit:Angela Wylie

That includes the permanent rotational placement of what will be, by 2016, 2500 US marines in the Northern Territory.

Their presence in Australia is also to be at the centre of discussions in Perth next week between senior US and Australian politicians.