French President Emmanuel Macron pledged to open up military records in a letter to an association of victims' families as they prepare to mark the 51st anniversary of the disaster near the southern city of Nice.
Many relatives have long suspected the Caravelle en route from Ajaccio on the island of Corsica was downed by a missile on September 11, 1968, during French military exercises in the area.
The official version blamed a fire on board that prompted pilots to lose control.
In March 2018, an investigating magistrate requested access to the secret files, saying the theory of an accidential missile launch needed to be taken "very seriously".
In a letter to Mathieu Paoli, president of the victims' association, which was seen by AFP, Macron wrote that he "understands your search to uncover the truth".
It added that he had asked Defence Minister Florence Parly to declassify documents if necessary and that the ministry was "pursuing its research to identify documents that might have been overlooked in previous investigations".
Paoli, whose parents were aboard the flight, has long sought to prove the authorities covered up a missile strike, citing claims from an ex-military officer and others.
Paoli and his brother also found the ship's log for the French Navy's Suffren missile launching ship, which was in the waters near Nice at the time, but discovered that the entry for September 11, 1968, had been torn out.
Ceremonies marking the disaster are scheduled in both Nice and Ajaccio this week.