The 30-year-old has experienced a woeful campaign with West Ham United, and Southgate has elected to start Everton's Jordan Pickford in tonight's friendly against the Netherlands. Nick Pope (Burnley) and Jack Butland (Stoke City) are also included in the Three Lions squad.
But Seaman thinks Hart should be getting the nod instead of his younger teammates.
"For me, Joe has got everything a goalkeeper needs," the Arsenal legend told talkSPORT.
"He's got all that experience, and you don't just disregard that; he's got 75 caps and played in the Champions League.
"The problem Joe's got is he's not playing. I know he played the last game for West Ham, but he needs to play for the rest of the season.
"I think Joe will definitely be in the three [for the World Cup]; he's a quality goalkeeper and you don't disregard all that experience he's got.
"What if one of the young guys goes in and has a nightmare?
"You need experience to fall back on, but at the moment, I don't think Jack or Jordan are up to the standard of Joe yet."