Smith is nursing a wrist injury, while Starc is recovering from a groin soreness, both injuries sustained during the Ashes series in England.
With regular skipper Pat Cummins nursing a fractured wrist, all-rounder Mitchell Marsh will lead the white-ball side, who will play three one-dayers and five T20 matches in South Africa.
"The compacted Ashes series and the World Test Championship was a heavy load for the group, and we are taking a conservative approach to the build-up to the World Cup," chief selector George Bailey said on Friday.
"With the World Cup the priority of the squad, it was determined on advice that it was best for Steve and Mitchell to join the group in India by which time we expect them to be fully fit and available for the Indian ODI series, plus the World Cup warm-up fixture."
Australia will travel to India next month to play eight limited-overs matches before beginning their ODI World Cup campaign against the same opponents on October 8th in Chennai.
To fill the void created by Smith's unavailability, Marnus Labuschagne has been added to Australia's ODI squad for the matches against South Africa, the country of his birth.
In Starc's absence, fellow left-arm quick Spencer Johnson, who was picked originally in the T20 squad, is now in contention to make his debut in both white ball formats.
Australia begin their South Africa tour with the opening T20 in Durban on August 30th.
