PORT-AU-PRINCE, Haiti (AP) _ Former President Jimmy Carter spent five hours in Haiti on a visit Friday in support of December general elections here.

''The elections this year will be successful. They will be honest and free and open, and also safe,'' Carter said in an interview with the independent Radio Haiti-Inter.

Elections are scheduled for Dec. 16. Carter was on his way to Guyana, the South American country where preparations for elections are also being made.

He arrived by private plane at International Airport and was welcomed by Foreign Affairs Minister Paul Christian Latortue. Carter paid courtesy calls on President Ertha Pascal-Trouillot and army chief of staff Lt. Gen. Herard Abraham.

In the company of Electoral Council President Jean-Robert Sabalat, Carter inspected voter-registration bureaus in the capital.

Carter said registration in rural areas was very good, but in some parts of the capital ''not many people have registered yet.''

This poor Caribbean island nation has 3 million potential voters. In 1987, during the last attempt at free general elections, 75 percent of eligible voters registered. The election collapsed when thugs supported by the army shot and hacked to death at least 34 voters. Hundreds were killed and wounded in pre-election violence.

The three-week voter-registration period began Oct. 5.

Carter arrived at 9:30 a.m. and left for Guyana at 2:30 p.m.

It was his third visit to Haiti since Mrs. Pascal-Trouillot's provisional government took power in March. He had visited Haiti in October 1987.

''The army is giving full support to the election this time,'' Carter said.

The president-elect will be sworn in on Feb. 7, 1991, on the fifth anniversary of the overthrow of dictator Jean-Claude Duvalier.

Elections will be monitored by the United Nations, the Organization for American States, the Caribbean Community and Carter Center observers. Carter said he would return himself in December.

He was accompanied on Friday by his wife Rosalynn and by Robert Pastor, Latin American specialist at the Carter Center.