With Castro at his side during a visit to Cuba, Chavez said it was US President George Bush who was the real threat to world peace, calling him the "lord of war" because of US military involvement in Iraq.
Chavez, who often accuses Washington of plotting to overthrow his populist government, said Venezuela would come to Cuba's defence if the United States invaded the communist-run island.
US Defence Secretary Donald Rumsfeld last week accused oil-exporter Venezuela and its ally Cuba of trying to destabilise Bolivia, where indigenous revolts have overthrown two presidents in two years.
"The truth is they [the Bush administration] are the great destabilisers in the region," Chavez said, blaming US-backed military coups and free-market economic policies for political instability in Latin America.
Chavez spoke for five hours on his weekly Venezuelan television show broadcast, live from the town of Sandino, 220km west of Havana in westernmost Cuba, where Venezuelan troops had built 150 prefabricated houses after Hurricane Ivan in September.
"We want peace ... We will do everything humanly possible to avoid an imperialist aggression"
"We want peace ... We will do everything humanly possible to avoid an imperialist aggression. But if it occurs to some madman, he will find these young men (Venezuelan soldiers) and us in command defending the independence and sovereignty of this land," Chavez said.
A billboard of Marxist revolutionary Che Guevara served as a backdrop for the two loquacious leaders.
Clad in military fatigues, Castro and Chavez drove in an open Soviet-made army jeep from Pinar del Rio to Sandino, where cheering residents lined the streets waving Cuban and Venezuelan flags to symbolize the growing political and economic ties between their countries.
US senator's comment
Chavez and Castro praised US Senator Arlen Specter for urging Rumsfeld to lower his rhetoric.
The Senate Judiciary Committee chairman and Pennsylvania Republican, who met Castro and Chavez separately last week, wrote to Rumsfeld on Friday asking for a "moratorium on adverse comments on Venezuela" to win back Venezuelan support in fighting the narcotics trade.
Chavez read out Specter's letter and asked Castro what he thought. "Very good," Castro replied jokingly in English.
Chavez suspended cooperation with the US Drug Enforcement Administration on 7 August, saying DEA agents where spying on Venezuela. Washington retaliated by revoking US visas of three Venezuelan military officers it suspects of involvement in drug trafficking.
"We are not conspiring, nor do we want to destabilise any government or any region," Castro said on Saturday at a meeting he hosted with Chavez and five Caribbean prime ministers to discuss a plan for Venezuelan oil supplies on generous terms.
Rumsfeld accused Venezuela and
Cuba of trying to destabilise Bolivia
Venezuela has become an economic lifeline for Cuba by shipping 90,000 barrels a day of oil, which Havana is paying for with medical services.
Chavez, Panamanian President Martin Torrijos and the five Caribbean leaders were in Cuba to attend the graduation of 1610 doctors from 28 countries trained by Cuba free of cost.