Chavez, a socialist, separately told a TV station if he were a U.S. citizen, he would vote for President Barack Obama in November and was sure if Obama were Venezuelan, he'd vote for Chavez.
On the last official day of the presidential campaign, an estimated 800,000 to more than 1 million supporters of center-right candidate Henrique Capriles filled the entire length of Caracas' 1.25-mile-long Avenida Bolivar, inspired by Paris' Champs Elysees, and spilled into several other avenues and boulevards, the normally pro-Chavez Ultimas Noticias reported.
The opposition was expressly forbidden by Chavez to use the politically emblematic avenue until June 10, when hundreds of thousands of people accompanied Capriles to officially register his candidacy for Saturday's presidential vote -- which polls indicate will be the closest election since Chavez took power in 1999.
Posters showed Capriles' slogan, "There is a way." One poster caricatured Chavez and said, "Can you imagine another six years?" the Spanish newspaper El Pais reported.
"This is undoubtedly the greatest concentration of people in the history of Caracas," Capriles, of the Justice First Movement, told the excited crowd, adding that supporters wearing the yellow, blue and red of the Venezuelan flag were dressed for Venezuela's "future progress."
"Progress is security, employment, opportunities and peace," he declared.
He tempered his remarks by speaking of three opposition campaigners killed by gunmen in a van during a campaign rally in Chavez's home state of Barinas Saturday.
Justice Minister Tareck El Aissami said Sunday a suspect and six accomplices in the killings had been arrested. The accomplices -- three men and three women -- are members of Chavez's United Socialist Party of Venezuela, Spain's Europa Press reported.
One of the accomplices is the nephew of the Barinas director of Venezuela's Environment Ministry, the Venezuelan newspaper El Universal reported.
Socialist Party Vice President Diosdado Cabello said Sunday the party had nothing to do with the killings, Venezuela's Globovision news network reported.
Capriles, 40, told his supporters the killings "should never have happened," and added, "I want to tell their families, and those angels in heaven, that we are going to defeat violence on Oct. 7."
Criminal violence is a key Capriles campaign issue. Oil-rich Venezuela, with a population of 28 million, is one of the world's most violent countries.
Other Capriles campaign issues include overcoming Chavez regime corruption, bureaucracy and inefficiency and combating the country's 18.6 percent inflation rate.
Capriles, governor of Venezuela's No. 2 state of Miranda, which includes part the metropolitan Caracas, has never lost an election.
Chavez, 58, told supporters in the northwestern city of Cabimas Sunday, "If I fail for faults I make as a human being, I am here in front of you with my morals intact."
"I didn't cheat you, I didn't fail you," he said. "Chavez is not for sale and Chavez does not give up."
He separately told the privately owned Televen TV network, "If I were from the United States, I'd vote for Obama."
He said he hoped his endorsement "doesn't harm Obama." He added, "Obama is a good guy" and "I think that if Obama was from Barlovento or some Caracas neighborhood, he'd vote for Chavez."
Barlovento is a Caribbean city of 200,000 founded by former African slaves.