Blackwater has come under intense scrutiny in recent years for its employees’ involvement in a 2007 Baghdad shooting in which 17 Iraqi civilians were killed, and other allegations.

The ruling was prompted by a DynCorp International Inc., Blackwater’s biggest competitor, which challenged the Army’s specifications for the $1.6 billion contract to train Afghan police.

The Government Accountability Office, a congressional audit agency, said the Army must give DynCorp an opportunity to bid on the contracts or explain in writing why it has excluded the company from competing, especially as DynCorp already provides police training in Afghanistan and Iraq.

The decision by the GAO leaves unclear who will oversee training of the struggling Afghan National Police, a poorly equipped, 90,000-strong paramilitary force that will inherit the task of preserving order in the country after NATO troops depart.

The contracts are part of a much larger contract the Army announced in 2007 that could be worth as much as $15 billion over five years to provide training to fight narcotics trafficking.

The Pentagon’s decision to allow Blackwater — which has rebranded itself as Xe — to run the training program drew a strong protest last week from Carl M. Levin (D-Mich.), chairman of the Senate Armed Services Committee.

Levin cited a history of allegedly abusive behavior by the contractor’s employees, including misappropriation of government weapons and hiring of workers with criminal records that included assault and drug offenses.

He also accused managers of the private security company of lying to win lucrative jobs in Afghanistan.