Amanda Knox -- Heavy Security Plans for U.S. Arrival

Amanda Knox and her family will be arriving in Seattle in the next few hours ... and TMZ has learned multiple security agencies, including U.S. Customs and the TSA are working together to execute a safety plan.

TMZ spoke with Port of Seattle Police spokesman Perry Cooper -- who tells us the Knox family contacted authorities to ask for the extra help ... and also to request a media area be set up so they can make a statement once the family touches down.

Amanda has been locked up in an Italian prison since 2007 -- when she was first suspected of killing her roommate, Meredith Kercher. Knox was cleared of the murder yesterday -- and she was immediately released from custody.

Cooper tells us the TSA, U.S. Customs and Border Patrol, Airport Police and the Port of Seattle Police will all take part in the security effort.

Cooper notes that while the safety of the Knox family is important, officials believe the main concern is keeping the entire airport secure.