"They're trying to do here what they were doing in Bolivia," Chavez said, accusing Washington of trying to oust him. "That's enough ... from you, Yankees," he said during a televised rally, using an expletive.
The socialist leader said Venezuela's ambassador to Washington, Bernardo Alvarez, would return to the U.S. "when there's a new government in the United States."
The move by Chavez brings relations with Washington to a new low and raises questions about whether the diplomatic clash could hurt trade. Venezuela is the fourth-largest oil supplier to the United States, and Chavez threatened on Thursday to cut off crude shipments "if there's any aggression against Venezuela."
He has made similar threats in the past, but the United States is his No. 1 oil client and taking such an action would debilitate his government financially.
Chavez, long at odds with Washington, appeared to leave open the door for restoring full relations once President George W. Bush's successor is in the White House.
"Hopefully, sooner than later, (the U.S.) will have a government that respects the peoples and the governments of Latin America," Chavez said.
Chavez warned last month that Duddy could soon be "packing his bags" after the diplomat lamented that U.S. and Venezuelan officials have not been cooperating in the war on drugs.
Duddy has said that deteriorating diplomatic relations between Caracas and Washington were giving drug smugglers the upper hand. Chavez announced the decision to oust Duddy hours after saying his government had detained a group of alleged conspirators in a plot to overthrow him. He accused the group of current and former military officers of trying to assassinate him with backing from the United States.
U.S. officials have repeatedly denied Chavez's accusations of backing plots against him.
Asked about Chavez's remarks, U.S. Embassy spokeswoman Jennifer Rahimi said: "We saw the speech and we're investigating, but we haven't seen anything official."
Tensions between Venezuela and the U.S. grew this week after two Russian strategic bombers were deployed to the country at Chavez's invitation.
"The presence of those Russian planes in Venezuela is a warning," Chavez said. "There's nothing better to keep yourself from being attacked than to dissuade."
The president said that behind the conspiracy to overthrow him were "the same coup-plotters" who masterminded a failed 2002 coup - which he also blamed on the Bush administration.
Chavez ordered an investigation of the alleged plot, which he said involved an active vice admiral and other former military officers. He said his intelligence services had been "following this for some time."
Military prosecutors were questioning several officers about their alleged involvement, Defense Minister Gen. Gustavo Rangel Briceno said.
Chavez ally Mario Silva, who hosts a program on state television, first played recordings of the purported coup plotters' phone conversations late Wednesday. It was unclear when they were recorded.
In one, a voice identified as an ex-officer said "we're going to take" the presidential palace. In another, a voice identified as retired air force Gen. Eduardo Baez Torrealba said "there is a pilot who has 1,000 hours in an F-16" - allegedly to be used in the plot.
Chavez said the authorities have known for some time that the conspirators were "looking for ground-to-air missiles ... to try to blow up the presidential plane ... or bomb the (presidential) palace with a plane."
Associated Press writers Ian James and Fabiola Sanchez contributed to this report.