Which US president signed and created the Orderly Departure Program of 1979 for people leaving Vietnam?
In the United States, no one created this program. It was not an effort by the United States government. The US government, of course, allowed Vietnamese immigrants to enter the country under certain conditions, but the Orderly Departure Program itself was not a US government initiative.
This program came about as an agreement between the United Nations and the government of Vietnam. Vietnamese had been leaving in large numbers in very unsafe ways because they were not allowed to leave by their government. In 1979, the government agreed to allow a more orderly process so that it would not look so bad in the eyes of world opinion.
Though the ODP was not a US government initiative, the US government supported it. Since this happened in 1979, the ultimate responsibility for actions taken to make this program work belonged to President Jimmy Carter. He would have signed any laws or executive orders connected to this program.