Hagel approved the order after speaking with French Minister of Defense Jean-Yves Le Drian Monday night from Afghanistan where he was visiting troops. Le Drian asked the US to help get African troops quickly into the country to prevent the violence there from spreading, said Pentagon spokesman Carl Woog.
There are more than 1,000 French troops in the Central African Republic, where more than 400 people were killed in two days of violence last week between Christians and Muslims. Christian armed fighters oppose the Muslim ex-rebels now in charge of the former French colony.
Woog said Hagel directed the US Africa Command to begin transporting forces in coordination with France because the US believes immediate action is needed to avert a humanitarian catastrophe. And he said the Pentagon will be evaluating what other U.S. resources might be available if additional requests for assistance come in.
Hagel's order came hours before President Barack Obama recorded an audio message urging calm in the Central African Republic.
Obama taped the message Monday in Dakar, Senegal, as Air Force One was refueling on its way to South Africa for a memorial service honoring former President Nelson Mandela, who died last week.
Addressing his remarks to "the proud citizens of the Central African Republic," Obama said citizens have the power "to choose a different path" than violence.
Those who commit crimes should be arrested, Obama said, adding that the United States will support the efforts of African countries and the French to restore security and protect civilians.
The transport flights are expected to begin in a day or two, according to a senior defense official who was not authorized to speak by name about the planning and thus requested anonymity. The official said there would be no other US troops on the ground except any air crew needed for the flights into the Central African Republic.
AP White House Correspondent Julie Pace, aboard Air Force One, contributed to this report.