The NL champions gave Bellinger a $233,900 salary in the minor leagues in the unlikely event the first baseman is sent down. Seager's minor league salary under the renewal is $287,500.
Bellinger made his big league debut April 25 and hit .267 with an NL rookie-record 39 homers and a team-high 97 RBIs. He will not be eligible for salary arbitration until after the 2019 season.
Seager's contract also was renewed by the Dodgers last year, when the shortstop earned $575,000. He hit .295 with 22 homers and 77 RBIs in 2017. He will be eligible for arbitration next winter.
The Dodgers reached agreements with third baseman Kyle Farmer ($547,500/$88,900); outfielders Andrew Toles ($555,000/$270,000) and Alex Verdugo ($547,500/$88,900); right-handers Ross Stripling ($555,000/$256,100), Dylan Baker ($547,500/$88,900) and Wilmer Font ($550,000/$88,900); and left-handers Scott Alexander ($555,000/$258,100) and Adam Liberatore ($565,000/$247,400).