Opponents accuse Chavez of being autocratic
Navy vice-admiral Carlos Molina Tamayo accused Mr Chavez and his allies of seeking to impose a totalitarian regime in Venezuela.
He said the president was damaging the nation's interests by soliciting closer ties to Cuba and other communist or leftist governments while steering it away from traditional allies such as the United States.
Admiral Molina Tamayo's criticisms followed calls for Mr Chavez to quit by other officers.
Those comments sparked protests by thousands of people who marched to the presidential residence demanding Mr Chavez's resignation.
Armed forces chiefs have insisted their troops remain loyal to the president.
Admiral Molina Tamayo urged more colleagues to join the opposition to the president, whose popularity has declined since he was elected by an overwhelming majority in 1998.
"I publicly state my rejection of the conduct of President Chavez and his regime," said the naval chief, serving as the ambassador to Greece.
Admiral Molina Tamayo is the highest-ranking officer to demand that Mr Chavez, a former army paratrooper, resign.
He urged Venezuelans to save their democracy. He condemned:
"We demand a truly democratic system," he said.
If Mr Chavez refused to stand down, the Supreme Court should put him on trial, the admiral said.
Capital flight
"I am calling on the national armed forces and the people to publicly show their opposition to Hugo Chavez's unpatriotic stand and for them to demand his resignation," he said in Caracas, reading from a prepared statement.
"It is absolutely essential that all parts of society join forces in this effort to recover our national dignity and freedom, demanding the establishment of a genuine democratic system."
His demands were likely to fuel more uncertainty about Venezuela's political and economic prospects.
Millions of dollars were sent abroad in a capital flight after demands for Mr Chavez's resignation earlier this month by an air force colonel, Pedro Sota, and a national guard captain, Pedro Flores, who claimed to be speaking for most of Venezuela's armed forces.