WASHINGTON — Blackwater Worldwide, the security contractor blamed by an angry Iraqi government for the shooting deaths of 17 civilians, is not expected to face criminal charges — all but ensuring the company will keep its multimillion-dollar contract to protect U.S. diplomats.

Instead, the seven-month-old Justice Department investigation is focused on as few as three or four Blackwater guards who could be indicted in the Sept. 16 shootings, according to interviews with a half-dozen people close to the investigation.

The final decision on any charges will not be made until late summer at the earliest, a law enforcement official said. All spoke on condition of anonymity because they were not authorized to publicly discuss the investigation.

The State Department publicly raised the question of Blackwater’s corporate liability last month when it extended the company’s contract by one year. The contract could still be canceled if criminal charges are brought, but the department said it was unlikely to penalize the corporation if only its employees were charged.

“I think that’s really what the FBI investigation needs to look at: Is the company culpable or are the individuals culpable?” Greg Starr, the department’s top security officer, said last month.

Justice Department spokesman Dean Boyd declined to comment.

Blackwater spokeswoman Anne Tyrrell said, “If it is determined that there are any individuals who need to be held accountable, we support that.”

The shootings began when a Blackwater convoy, which was responding to a Baghdad car bombing, entered the Nisoor Square traffic circle. Blackwater says the convoy was ambushed by insurgents, touching off a firefight. Iraqi witnesses, however, described an unprovoked attack in which security guards fired indiscriminately, killing motorists, bystanders and children in the square.

The shooting enraged the Iraqi government, which originally sought to expel the company from the country, and strained diplomatic relations between Washington and Baghdad. The shooting also raised questions at home and abroad about the U.S. reliance on heavily armed private contractors in war zones. With nearly 1,000 personnel working in Iraq, Blackwater is the largest State Department security contractor; critics have compared its guards to mercenaries.

Since the shooting, Blackwater has also come to symbolize the legal gray area in which such security contractors operate. Iraqi officials wanted to charge Blackwater guards in Baghdad, but U.S. contractors are immune from prosecution in Iraqi courts. U.S. prosecutors believe they have jurisdiction to bring a case in Washington, but that’s an untested legal theory.

This week, the Justice Department continued its secret grand jury interviews in the case with the testimony of a U.S. military official. An estimated 40 witnesses have so far been brought before the grand jury in Washington, including Blackwater security guards and company managers. Iraqi witnesses also are expected to testify in coming months, according to people close to the case.

Companies are sometimes charged for the wrongdoing of their employees, but the standard is high. Prosecutors must prove that the corporation — not just the employees — intended to break the law. One recent example is Chiquita Brands International, which was fined $25 million after admitting it paid Colombian terrorists to protect its most profitable banana-growing operation.

“The law tries to get at the idea of moral responsibility,” said longtime Washington corporate lawyer Thomas F. Cullen. “To be morally responsible for someone else’s criminal act, you need to be somehow involved in their criminal intent. Did you direct it?”

Blackwater could still face charges if, for example, prosecutors conclude the company lied to investigators, destroyed documents or obstructed the probe. Blackwater says it is fully cooperating with the Justice Department. The Department gives credit for such cooperation when deciding whether to bring charges.

Even if Blackwater avoids prosecution for the shooting, its legal problems will continue.

Families of the Nisoor Square victims are suing Blackwater under a wrongful death claim in civil court. The lawsuit does not specify how much money they are seeking from Blackwater, its 11 subsidiaries and founder, Erik Prince, all of whom are named as defendants. The standard of proof needed to win is lower in civil cases than in criminal cases, which require proof beyond reasonable doubt.

Separately, federal prosecutors in North Carolina are investigating whether Blackwater played a role in a weapons smuggling case linked to the Kurdish militant group PKK, a U.S.-designated terrorist organization. Blackwater denies involvement in the case.