Chavez told thousands of supporters on Saturday that he thought "Hitler would be like a suckling baby next to George Bush".
He was responding to comments made on Thursday by Donald Rumsfeld, the US Defence Secretary, comparing Chavez to the Nazi leader.
Chavez was speaking at a rally in Caracas to commemorate a failed 1992 coup that he led as a lieutenant-colonel. He said: "The imperialist, genocidal, fascist attitude of the US president has no limits."
He said that Washington was considering invading Venezuela and that the country therefore needed more weapons to defend itself.
"We still need a higher number of rifles," he said. "The Russian rifles are not enough. Venezuela needs to have one million well-equipped and well-armed men and women."
Chavez was referring to Venezuela's purchase of military equipment, including 100,000 Russian-made machine guns.
"The imperialist, genocidal, fascist attitude of the US president has no limits"
Chavez told the crowd of cheering supporters he had started making contacts with other countries which would be able to supply the additional rifles.
Washington and Caracas recently clashed over a US block on sales of Spanish military equipment to Venezuela.
The Spanish aircraft contained US-made technology, which requires countries to get Washington's clearance for the sale.
Ties with the US and the socialist leader had already worsened further this week after Chavez expelled US naval attache, John Correa, for allegedly passing secret information from Venezuelan military officers to the Pentagon.
Chavez has said he could shut Venezuelan oil refineries in the United States and sell elsewhere if Washington decided to end diplomatic ties.
Flush with cash from high crude oil prices, Chavez is promoting socialist reforms at home and aggressively challenging US free-market proposals by allying himself with his South American neighbours, as well as Cuba and Iran.
US officials have made no suggestion they plan to break relations.
Washington has repeatedly dismissed Chavez's threats and charges, including numerous claims that the US is attempting to overthrow him, as inflammatory rhetoric directed at stirring up nationalist sentiment among his poor supporters.
Rumsfeld on Thursday likened
Chavez to Hitler
Elsewhere in Caracas on Saturday, thousands of opposition sympathisers marched to protest against what they perceive as increasing authoritarianism under Chavez and strongly condemned the bloody coup attempt he led 14 years ago.
More than 80 civilians and 17 soldiers were killed on 4 February 1992, before troops put an end to the putsch.
Chavez has celebrated the rebellion's anniversary every year since he took office in 1999.
Some Chavez critics feel he is taking Venezuela on the road to Cuban style communism.
Chavez met close ally Fidel Castro on Friday.