NEW YORK -- Brazilian President Fernando Collor de Mello has launched a campaign to turn his country's nuclear program to strictly peaceful purposes, a move that may put him at odds with his own military.

In a speech to the U.N. General Assembly on Monday, Collor called for a ban on test nuclear explosions, even for "peaceful" purposes, in Latin America and the Caribbean. Last week, Collor flew to the Amazon state of Para to order the closing of a deep shaft that had all the markings of a nuclear test site.

In an interview here shortly after his U.N. speech, Collor and some of his cabinet ministers said the closing of the steel-and-concrete-lined shaft, which was more than 1,000 feet deep and nearly 4 feet wide, was designed to lay to rest reports that Brazil has been engaged in a clandestine program to build a nuclear bomb. The shaft reportedly was drilled by the air force when Brazil was under military rule before 1985, but Collor would not confirm this.

"It's very difficult to know when, how, who was responsible" for drilling the shaft, Collor said. "It is a very sensitive issue. . . . Times have changed. The important thing is that the shaft is being covered up with concrete and that we are not going to enter into any nuclear adventure in Brazil. We are embarked on a profound reevaluation of the entire nuclear program."

"This is very positive movement," said Leonard Spector, an expert on nuclear proliferation with the Carnegie Endowment for International Peace. "He has actually thrown down the gauntlet to the military."

Adm. Maximiano Eduardo da Silva Fonseca, a navy minister in the military government during the early 1980s, said in an interview published Monday in Sao Paulo that he favored the explosion of one atomic bomb to show that Brazil has the capability to be a nuclear military power.

Last year, Brazil mastered the technique for enriching uranium in the laboratory, indicating that it has the technological capability to develop a bomb, according to Spector, author of "Nuclear Ambitions," a book about expanding nuclear weapons capability in the Third World published this month.

In his U.N. speech, Collor called for amending the Tlatelolco Treaty of 1967, which prohibits nuclear weapons in Latin America, to ban all nuclear explosions. But Brazil, like neighboring Argentina, has refused to sign the Nuclear Non-Proliferation Treaty.

The non-proliferation treaty "is a discriminatory treaty, which froze the world as the world was in 1970," Jose Goldenberg, Collor's secretary of science and technology, said in the interview here. "The signing of the treaty could hamper our progress in technology in this area."

Collor defended Brazil's arms sales to Iraq, arguing that only about "0.03 percent" of Iraq's arsenal is Brazilian-made and that most of those weapons are not as lethal as the ones sold by the major Western powers, such as bombs and chemical weapons.

He said a large part of the sales to Iraq consists of Toucan trainer planes. "And as you know," Collor said, "the toucan {referring to the bird that lends its name to the plane} is not a very good flier."

Brazil imported 160,000 barrels of oil a day from Iraq before a U.N. trade embargo halted that commerce after Iraq's invasion of Kuwait on Aug. 2, but Collor and his ministers said imports from Venezuela, Nigeria and Angola were making up for the Iraqi oil. Nevertheless, Goldenberg said, rising oil prices because of the Persian Gulf crisis are expected to cost Brazil up to $2 billion a year as it tries to revise the economy and renegotiate foreign debts.

Collor had warm words for President Bush's initiative for a free-trade zone and debt relief in Latin America, calling it welcome and innovative. He said his government and others in Latin America would be suggesting ways to implement it "so that it doesn't fall into a vacuum."