South Australian and Federal Police are preparing for another massive security operation with Hillary Clinton set to visit Adelaide next week.

The security surrounding Prince Charles and Camilla yesterday will appear just a dress rehearsal compared to when the United States Secretary of State Hillary Clinton arrives in South Australia.

7News understands about 140 rooms have been booked at the Intercontinental Hotel for Mrs Clinton and her entourage, including her staff and secret service agents.

They plan to arrive next Wednesday and stay for two nights, but some rooms at the hotel will be locked down before then so they can be made secure.

While the US Embassy is not confirming any details, it is understood planning for the trip is so advanced it is unlikely to be cancelled.

It is expected Mrs Clinton will attend top-level defence and foreign policy talks in Perth next Wednesday before meeting up with friends in Adelaide.