By Joseph Guyler Delva and Pascal Fletcher
PORT-AU-PRINCE (Reuters) - Exiled former Haitian President Jean-Bertrand Aristide headed back to his country on Friday after ignoring U.S. opposition to a homecoming some fear could disrupt Haiti's presidential election runoff on Sunday.
Aristide, 57, who lived in South Africa after his 2004 ouster that he says Washington helped engineer, was flying home to Port-au-Prince in a charter plane with his family and was expected to arrive by noon (1 p.m. EDT) on Friday.
He has insisted on returning home just before Sunday's decisive presidential contest, which the United States and Western donors want to see produce a stable leadership to steer Haiti's arduous recovery from a destructive 2010 earthquake.
U.S. officials say the presence of the charismatic, leftist former Catholic priest, who still has a passionate following in his poor Caribbean homeland, could be "destabilizing" for the election, which is being protected by U.N. peacekeepers.
U.S. President Barack Obama called his South African counterpart, Jacob Zuma, to stress the importance of Aristide not returning before the poll. South Africa said it could not stop Aristide from going back to his country.
The vote pits former first lady and law professor Mirlande Manigat against entertainer and music star Michel Martelly in a clash of contrasts that has enlivened the first second-round runoff in the history of Haiti's presidential elections.
Despite a generally calm second-round campaign, tensions and rhetoric have heated up and there are fears Aristide's potentially divisive presence and large numbers of his followers in the streets could stir up a volatile electoral atmosphere in one of the world's poorest states.
"Haiti needs political stability to move ahead with development efforts," Ambassador Albert Ramdin, assistant secretary general of the Organization of American States, said in a statement appealing for calm in the election.
Aides to Aristide say he intends to stay out of politics and use his expertise in education to assist in Haiti's recovery from the earthquake, which will require billions of dollars of foreign donor funds.
Both presidential candidates have said Aristide has the right as a citizen to return to his country, although they would have preferred him to come back after Sunday's vote.
Haiti's government said it had drawn up a security plan in the expectation Aristide's return would generate crowds.
EXPECTED WARM WELCOME
His supporters were preparing to give him a warm welcome, and banners welcoming "Titide" -- as he is affectionately known by many Haitians -- have been strung across the streets of the capital, which still bears the scars of the 2010 earthquake.
"President Aristide is a strong leader who doesn't take orders from a superpower such as the United States," said Johnny Mazart, 36, a carpenter. "That's why they ousted him, because he listened to the Haitian people, not foreigners."
Aristide became Haiti's first freely elected president in 1991, but was overthrown after seven months. Re-elected in 2000, his second term saw economic instability and violence.
Flown into exile aboard a U.S. plane after a rebellion toppled his government in 2004, Aristide has described his departure as a "kidnapping." His supporters say Washington worked to keep him in South Africa away from his homeland.
Despite assertions by aides he will stay out of politics, some believe he may seek to reunite his Fanmi Lavalas party, Haiti's biggest, which was barred by electoral authorities from fielding a candidate for the elections on grounds it did not satisfy registration rules.
Some commentators said Washington's bid to keep Aristide out of Haiti before Sunday's vote was a mistake.
"Aristide's return marks an end to the era when the United States gets to choose the political leaders of other countries. It is a historic victory for democracy and self-determination," said Mark Weisbrot, co-director of the Washington-based Center for Economic and Policy Research.
(Additional reporting by Donald Wilson and Faradjine Alfred; Editing by Peter Cooney)