Arlington-based CACI International secured a long-fought victory Wednesday when a federal judge dismissed a lawsuit alleging its employees directed mistreatment of detainees at Abu Ghraib prison in Iraq.

The judge did not explicitly rule on CACI’s role in the alleged abuse, instead deciding that because the incidents happened overseas, the U.S. District Court in Alexandria does not have jurisdiction to hear the case.

The decision, which the plaintiffs have vowed to appeal, could have broad implications for the growing corps of contractors who accompany U.S. troops around the world and are tasked with sensitive jobs. CACI’s employees, who conducted interrogation and other tasks at the Iraqi prison, were accused of being part of a group of conspirators who allegedly abused and tortured four detainees between 2003 and 2004.

U.S. District Judge Gerald Bruce Lee ruled that CACI is “immune from suit for claims arising from acts related to its contract or performed in connection with military combat operations.”

The case is likely to spark renewed debate about the proper role of government contractors and what legal protection they should receive when acting on behalf of the military.

The ruling is “troubling,” said Noah Feldman, a professor at Harvard Law School and a constitutional adviser to the Coalition Provisional Authority in Iraq in 2003.“The court is saying, ‘We’re never going to look into it. We don’t want to know what happened in Abu Ghraib,’ ” Feldman said.

CACI, one of the region’s largest defense contractors, has been unusually public in defending itself against the former detainees’ allegations. In 2008, J. Phillip “Jack” London, CACI’s executive chairman, went so far as to publish a book titled “Our Good Name: A Company’s Fight to Defend Its Honor and Get the Truth Told About Abu Ghraib.” Even after Chantilly-based contractor Engility paid $5.28 million last year to settle with former Abu Ghraib inmates in a similar case, CACI showed no signs of relenting.

In a statement Wednesday, the company said it is “gratified by the court’s decision and hope[s] this is the end of these baseless lawsuits.”

CACI contended that the case should not be argued in Virginia, because the allegations concerned actions that occurred in Iraq and as a U.S. government contractor, CACI is immune under Iraqi law. The company also cited an April Supreme Court case that found that the Alien Tort Statute — under which most of the claims against CACI were brought — does not apply to actions outside the United States.

Baher Azmy, the attorney for the plaintiffs, had called CACI’s interpretation of the Supreme Court ruling “implausibly simplistic.” The detention center run by the U.S. government constituted U.S. territory, he argued.

But Lee disagreed. The “alleged conduct giving rise to their claims occurred exclusively on foreign soil,” he said in his decision.

The dismissal reveals a “blind spot” in U.S. law, said Jonathan Turley, a George Washington University law professor who has argued national security cases.

“We talk a good game about our government being subject to the rule of law, but we have created this expanding exception where the government and its contractors can shield the worst possible abuses,” Turley said. “The government and its contractors are virtually without a check or balance in our system.”

Azmy said the plaintiffs will appeal the dismissal. “It’s a disappointing decision,” he said. “I think [it] seriously misreads the Supreme Court’s . . . decision and in effect creates lawless spaces that give human rights abusers impunity even in U.S. courts and even if they reside here.”