BRASILIA, Brazil -- After conducting an internal investigation, bringing in senior staff and briefing members of Congress, the U.S. Air Force expects this month to restart a contentious competition to purchase single-engine turboprop attack aircraft for Afghanistan that pits the Brazilian company Embraer and its A-29 Super Tucano against Wichita, Kan.,-based Hawker Beechcraft and its AT-6.

Embraer, however, is concerned about getting a fair shake in the new competition, the outcome of which will affect not only the two companies, but also possibly the future of growing Brazil-U.S. military cooperation as well as the prospects for U.S. defense companies seeking to do business in Brazil.

In March the Air Force abruptly canceled a $355 million contract it had just awarded Embraer to build 20 light air support aircraft for the Afghan air force after losing bidder Hawker Beechcraft sued the Pentagon. A subsequent internal Air Force investigation reportedly found internal administrative problems in the procurement process. The contract was rebid, with the final proposal due next Monday.

The U.S. Air Force expects to announce the new winner early next year, but the aircraft haven’t been requested for delivery until 18 months after that – as U.S. troops are supposed to be winding down their deployment in Afghanistan.

Unlike the original competition, the new one lacks a flight evaluation, in which the two planes would be flown under similar conditions. It also won’t accept data from the prior competition, a concern to Embraer. Hawker Beechcraft’s older planes, such as its T-6, are better known to U.S. military.

“They think that they are at a significant disadvantage because of a lack of a fly-off or use of prior data,” a senior staffer for a Florida member of Congress said, describing meetings with Embraer. The staffer, like several people interviewed for this story, spoke only on the condition of anonymity because of the sensitivity of the issue.

Officials on both sides acknowledge that the handling of the contract has hurt a bilateral defense relationship that “has advanced pretty dramatically,” said the U.S. ambassador to Brazil, Thomas Shannon.

Brazil has long harbored resentment over what it sees as slights in the way it’s treated in military matters. Past Brazilian officials thought the country never got the recognition it deserved for sending troops to fight alongside the Allies in World War II. Brazil also is still smarting over its abandonment of its nuclear weapons program under U.S. pressure, only to see India develop nuclear weapons and continue to resist signing the Nuclear Non-Proliferation Treaty while still receiving favorable treatment from Washington.

In recent years, U.S. officials have tried to improve defense relations with Brazil, the largest country in South America and the world’s sixth largest economy. A 2010 agreement that originated in the George W. Bush administration called for increased sharing of military systems and equipment.

The chairman of the Joint Chiefs of Staff, Army Gen. Martin Dempsey, visited the country in March and Defense Secretary Leon Panetta visited in April, launching the U.S.-Brazil Defense Cooperation Dialogue with Brazilian Defense Minister Celso Amorim.

Marco Aurelio Garcia, a foreign policy adviser to Brazilian President Dilma Rousseff, said: “We have a very good relation with the U.S. and we want to continue to develop it. But a decision like this creates problems not only in military relations but in economic and commercial relations.”