The Manchester United striker, 37, has not been first choice for his club this season but will be part of his country's bid to win the tournament for the first time.
"All the players I have called up come with the hunger to win and make Portugal world champions, Ronaldo included," Santos said.
Ronaldo, the captain and all-time leading goalscorer in men's international football with 117 strikes, has plenty of younger supporting teammates, including Atletico Madrid's Joao Felix and AC Milan's Rafael Leao.
Santos, who led Portugal to Euro 2016 glory in France, left Paris Saint-Germain midfielder Renato Sanches out of the squad and called up Benfica center-back Antonio Silva, 19, as well as veteran 39-year-old Pepe.
Wolves midfielder Joao Moutinho, 36, who has appeared for his country 146 times, more than any other player apart from Ronaldo, was not included nor was his teammate Goncalo Guedes.
Portugal open their World Cup campaign in Group H against Ghana on November 24 before facing Uruguay on November 28 and South Korea on December 2.
