SAO PAULO, Brazil (AP) -- Brazil's refusal to allow the International Atomic Energy Agency to fully inspect one of its nuclear facilities has heightened suspicions about its commitment to nonproliferation.

Although Brazil signed the Nuclear Nonproliferation Treaty in 1997 and said its nuclear program has peaceful objectives, suspicions over its commitment have simmered for more than a year.

They came to a head last week after the government confirmed that IAEA inspectors were denied access in February and March to uranium-enrichment centrifuges at a facility under construction in Resende, near Rio de Janeiro.

It cited the need to protect industrial secrets and said the centrifuges were, and will remain, off-limits for visual inspection.

Science and Technology Minister Eduardo Campos told The Associated Press that Brazil had invested close to US$1 billion and years of research to develop its uranium-enrichment technology.

He said the performance of Brazilian centrifuges was 30 percent more efficient than those found in other countries.

"This is a technology we must protect," he said.

Centrifuges are used to enrich uranium for use in nuclear power plants or atomic weapons.

The doubts over Brazil's nuclear program were likely discussed during two days of closed-door meetings between Brazilian officials and U.S. Assistant Secretary of State for Nonproliferation, John Wolf.

Wolf left Brasilia on Thursday after two days of meetings of the Brazil-U.S. Joint Committee on Nuclear Energy Cooperation.

Brazil's uranium-enrichment program may also be discussed next week during a visit by U.S. Energy Secretary Spencer Abraham.

According to the U.S. State Department, those meetings should not be considered the result of "a reaction nor an expression of concern about Brazil's commitment to nuclear nonproliferation," said embassy spokesman Wesley Carrington.

But experts think concerns do exist over Brazil's commitment to nonproliferation.

"Brazil is beginning to be perceived as a country apparently wanting to reevaluate its commitment to nonproliferation and this is a big part of the problem at hand," said Jon Wolfsthal, deputy director for nonproliferation at the Carnegie Endowment for International Peace in Washington D.C.

Its refusal to allow the inspections came "in the middle of Iran's and North Korea's challenges to the IAEA's authority."

"Anything seen as undermining the IAEA's authority puts everyone on edge," Wolfsthal said.

Brazil's claim of protecting industrial secrets does not hold up because the IAEA has a "proven track record" of respecting such information.

Brazil's government laid plans for development of nuclear weapons technologies in the 1970s when the country was governed by a military dictatorship whose leaders were oriented by a stern "national security" doctrine and a traditional rivalry with Argentina, which was also developing similar technologies during its military regime. But the plans were abandoned when Brazil returned to democracy in the 1980s.

Suspicions about Brazil's nuclear program started months before Luiz Inacio Lula da Silva became president in January, 2003.

"Why should we be asked to use slingshots while others point their cannons at us? Brazil will only be respected when it is strong economically, technologically and militarily," Silva said about the Nonproliferation Treaty during a speech.

Six weeks later, as president-elect, Silva said his government would never consider building an atomic bomb and respect the treaty.

It was Brazil's refusal to allow inspectors to see the centrifuges that rekindled doubts, according to Mario Marconini, executive director of the Brazilian Center for International Studies in Rio de Janeiro.

"Given the tension-ridden international scenario that emerged after September 11, one could understand the doubts concerning Brazil's commitment to nonproliferation," Marconini said.

Worries that Brazil's technology could fall into the wrong hands have also stoked international fears.

"People are concerned that Brazil could one day transfer its uranium-enrichment technology to so-called rogue states, or be unable to prevent it from being stolen," said Luis Bittencourt, Brazil Project Director at Washington D.C.'s Woodrow Wilson International Center for Scholars.

Brazil has the world's sixth largest uranium reserve and has had the capacity to enrich uranium since the 1980s, but has so far only done so for research purposes.

The first of four centrifuge units at Resende is to begin supplying Brazil's two nuclear power plants by the end of October. The plants produce about 4.3 percent of the electricity in this nation of 178 million people.

"By 2010, we expect to be producing 60 percent of the enriched uranium used at the two plants, meaning we will be saving close to US$12 million every 14 months," Campos said.

Uranium mined in Brazil is now enriched in Canada and Europe.

Brazilian officials hope by 2014 to be enriching enough uranium to run three nuclear power plants and have an exportable surplus.

One of Brazil's top nuclear scientists thinks Brazil should allow the IAEA inspectors to see the centrifuges.

"Even if Brazil's has some kind of new technology, I am sure that technology is not earthshaking enough to hide," Jose Goldemberg told The Associated Press.

Copyright 2004 The Associated Press.