MONTERREY, Mexico (AP) – Three former ministers in President Vicente Fox’s Cabinet vied Sunday to become his ruling National Action Party’s presidential candidate in 2006 elections.

Hundreds of voters in the center-right party’s primary filed into National Action headquarters in this northern industrial city for the first of three regional votes to select a presidential candidate. Fox is prohibited by law from seeking a second term.

The voting kicks off the primary season among Mexico’s three major political parties, which must register their candidates by January.

During 71 years of uninterrupted power – which ended with Fox’s historic victory in 2000 – Institutional Revolutionary Party, or PRI, presidents hand-picked their successors behind closed doors and the party conducted elections often marred by fraud.

This year, political parties already were tossing and turning over whom to back.

Among the contenders for Nation Action were former Interior Minister Santiago Creel, who had been the leading preference among party members, especially in the north. But after a televised debate last week, former Energy Minister Felipe Calderon gained a few points in opinion polls and was tied with Creel.

Former Environment Secretary Alberto Cardenas also was seeking the party’s nomination to be candidate for the presidency.

“We need to follow through with changing the country,” said Martin Lopez, 32, a public accountant from Monterrey. “I voted for Santiago Creel because I believe he can provide continuity to the government of Fox.”

National Action was choosing its presidential candidate via three regional elections in which an estimated 1.1 million party members are eligible to vote.

The winner will face the candidates of the PRI, which remains Mexico’s largest party, and the leftist Democratic Revolution Party, or PRD.

Former Mexico City Mayor Andres Manuel Lopez Obrador of the PRD leads all polls ahead of the presidential election and was expected to receive the party’s nomination Sep. 18 without contest.

Two people were seeking the candidacy of the PRI. Former Mexico state governor Arturo Montiel and former PRI party president Roberto Madrazo were scheduled to face off in a primary Oct. 30.

National Action members in 10 Mexican states, including Nuevo Leon, of which Monterrey is the capital, took part in Sunday’s vote. The second vote is Oct. 2, and the third is Oct. 23.

If no candidate obtains 50 percent plus one vote in the first phase a second round will be held Nov. 6 between the top two contenders.