The International Olympic Committee's (IOC) members have unanimously backed a plan to make a dual award of the 2024 and 2028 Games at their next meeting in September.
This means the usual seven-year gap between the award and staging of a Games will be waived for 2028, providing the IOC's executive board can reach a "tripartite agreement" with the two bidding cities, Los Angeles and Paris.
If a deal cannot be struck, the 131st IOC session in Peru's capital Lima will vote on the two bids for 2024 as normal.
The proposal was presented to the 130th session in Lausanne on Tuesday by IOC vice-president John Coates, who said the IOC was "recognising the exceptional circumstances and unique opportunities presented by the candidatures of Los Angeles and Paris".
The unanimous vote was welcomed by IOC president Thomas Bach and the mayors of Los Angeles and Paris, Eric Garcetti and Anne Hidalgo, who have been in Lausanne with their bid teams for last few days.
It is widely believed the French capital will be given the 2024 Games, the 100th centenary of its last Olympics, and its bid has been boosted by new French president Emmanuel Macron's support this week.
American president Donald Trump has not joined the LA bid in Switzerland, leaving the pitch to the likes of former Olympic champions Janet Evans and Michael Johnson, but he has tweeted that he is "working hard to get the Olympics for the United States".
Working hard to get the Olympics for the United States (L.A.). Stay tuned!— Donald J. Trump (@realDonaldTrump) July 11, 2017
If LA agrees to step aside and let Paris have the 2024 Games without a vote, it is expected to be given some financial assistance for the additional four years of host city-related costs. It will also give the Californian city more time to complete its already-scheduled transport infrastructure improvements, although its venues are all ready for use now.
The preference for Paris in 2024 is largely sentimental, based on the centenary issue, its longer wait for a Games (LA hosted them in 1980) and its three unsuccessful bids for the 1992, 2008 and 2012 Games. There are also some doubts about the land it needs for its Athletes' Village being available in 2028.
The decision to approved the principle of the dual award is a victory for Bach who has come under increasing pressure as cities have dropped out of bidding contests for Games in recent years.
Boston, Budapest, Hamburg and Rome have all pulled out of the race for 2024, turning it into a contest between two strong candidates Bach was determined not to squander, particularly after four cities withdrew from the race for the 2022 Winter Olympics and negative stories continued to come out of Rio about its uncertain Olympic legacy.