US Defense Secretary Leon Panetta has used his trip to Brazil to lift doubts about Washington's pledge on technology transfer if Brasilia buys Boeing's F/A-18 Super Hornet fighter jet.

Panetta, who ended a two-day visit on Thursday, sought to ease concerns that the United States could use technology transfer -- a key factor in Brazil's soon to be announced choice of which jet to purchase -- as a political lever.

The F/A-18 is competing against the French produced Rafale fighter and Swedish manufacturer Saab's Gripen aircraft for Brazil's contract for 36 next-generation fighter jets valued at between $4 billion and $7 billion.

Brazil, Latin America's dominant power and the world's sixth biggest economy, is now insisting on technology transfer in all its defense agreements.

Panetta on Wednesday offered Brazil "an unprecedented advanced technology sharing that is reserved for only our closest allies and partners."

"We fully understand that Brazil is not looking just to be the purchaser of a fighter aircraft, but rather a full-fledged partner in the development of cutting-edge aviation technology," he said in a speech at a military academy.

"With the Super Hornet, Brazil's defense and aviation industries would be able to transform their partnerships with US companies, and they would have the best opportunity to plug into worldwide markets," he added.

But Brazilian officials are wary of Washington's possible use of technology restrictions.

In 2006, the United States blocked the sale of 24 Super Tucano light attack aircraft made by Brazil's top aeronautics firm Embraer to Venezuela as they contained US-built components.

The Super Tucano is a turboprop aircraft used in counter insurgency, close air support, aerial reconnaissance missions and in pilot training.

In a joint press conference with Panetta in Brasilia on Tuesday, Brazilian Defense Minister Celso Amorim made it clear his government wanted the fighter jets it will buy to be produced locally.

Brazil is keen to develop its own defense industry and wants to assemble aircraft with foreign technology for export, a plan Panetta appeared to support subject to conditions, noting that such a stance amounted to a policy shift.

"There was a time when the United States discouraged developing military capability in countries in Latin and Central America," the US defense secretary said on Wednesday.

"Today, we think the development of those kinds of capabilities is important if we can use those capabilities to develop the kind of innovative partnerships that I'm talking about, to advance the security in this region," he added.

Panetta pointed out that Washington now rarely denies Brazil technology export licenses and had in fact granted it 4,000 in the past two years.

US officials said orders for its technology in Brazil had soared 139 percent since 2007.

A major irritant for Brazil, however, was the US cancelation of a $380 million contract with Embraer to buy 20 AT-29 Super Tucano aircraft for the Afghan army.

Embraer and its US partner Sierra Nevada were awarded the contract in December but the US Air Force called off the deal in February after a legal challenge from rival Hawker Beechcraft Corp.

The Pentagon has called for a new round of bidding for the contract, but in any case the equipment will not be delivered before 2014.

On Wednesday, Panetta also praised Brazil's rise on the global stage.

"This is a relationship between two global powers, and we welcome Brazil's growing strength. We support Brazil as a global leader and seek closer defense cooperation," he noted.

"We won't agree on every matter -- no two countries, not even the closest allies, ever do. But I do believe that our common interests are so great, and the possibilities that come from our cooperation are so tangible, that we must seize this opportunity to build a stronger defense partnership," he said.

The US defense secretary began his first Latin America tour in Colombia on Monday and he was also to visit Chile after leaving Brazil.