CARACAS, Venezuela -

Venezuelan opposition leader Henrique Capriles has stepped down from his post as a state governor to campaign against Hugo Chavez for the presidency.

Capriles is trailing in the polls in a race that so far has been dominated by speculation about Chavez's health.

The president has scaled back his public appearances after finishing his latest cancer treatments in Cuba, and it remains to be seen how active Chavez will be during the campaign.

Capriles spoke to hundreds of supporters at a stadium in Caracas on Wednesday as he formally handed over his office vowing to become Venezuela's next president.

He entrusted the governor's post to an aide, Adriana D'Elia.

The 39-year-old Capriles was chosen in a February primary to be the opposition's single challenger to take on Chavez.