Capriles said he wants to debate issues such as education, health care and crime.
"I challenge them. We're going to debate our government proposals. We're going to debate wherever they wish," Capriles said in a speech in eastern Monagas state.
Chavez said in a campaign speech in Caracas that Capriles and other opposition leaders are "the worst of the worst" and represent the interests of the wealthy and "fascism."
"Let's hope some new real political leaders of the right emerge," Chavez told a crowd of cheering supporters. "Let's hope they give Venezuela something we need: a serious, responsible ... opposition in order to be able to debate."
Chavez is running for another six-year term in the Oct. 7 vote and is expected to face the toughest re-election contest of his nearly 14-year-old presidency.
The leftist president has used strong insults against his rival throughout the campaign, and on Friday said Capriles comes from "a current of the far right ... Nazis, Nazis. It's pure fascism."
Capriles has previously responded to similar comments demanding respect for his family and the Jewish heritage of his late grandmother, a Holocaust survivor.
Speaking to supporters Friday, Capriles said his opponent has turned
"Whoever hurls insults, it's that his ideas have run out," said Capriles, who describes his views as center-left and favors combining social programs for the poor with a business-friendly approach.
Chavez told supporters that his rival has a hidden agenda to impose a package of right-wing measures "that would lead Venezuela to a civil war."
Venezuela has for years been heavily polarized between supporters and opponents of Chavez, and tensions have been on the rise ahead of the vote.
Jennifer McCoy, director of the Americas program at the Carter Center, said at a forum in Washington on Friday that there are some concerns in Venezuela about whether both sides are prepared to accept the results whatever the outcome. "Or will there be any situation in which there may be some unrest, even violence?" she said.
"In order to prevent the conditions that may produce a dangerous situation or potential for violence or severe instability, the basic thing that's needed is to provide mutual guarantees to both sides," McCoy said at the forum hosted by the Woodrow Wilson Center.
McCoy, who has directed past election-monitoring missions in Venezuela and other countries, said the potential for danger arises "when people fear that they will lose the benefits that they have gained, when people fear that they will be punished or recriminated against, and when they fear that they will be excluded in the future from participation."
"Hopefully the candidates will try to avoid these kinds of scenarios," she said.
Associated Press writer Ian James contributed to this report.