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The Rock already has a major celebrity supporter if he REALLY decides to run for the White House -- his old WWE buddy Dave Bautista ... who says Rock is a "better candidate than f**king Trump!"

The "Guardians of the Galaxy" star was at LAX when we started talking politics -- specifically about The Rock toying with the idea of running for president when he's finished dominating Hollywood.

"I'd vote for him," Bautista said ... "He's a decent person, decent human being, good leader, smart."