WASHINGTON - Federal prosecutors have issued grand jury subpoenas to some of the Blackwater employees present at a Sept. 16 shooting in Baghdad in which the company's security personnel are accused of killing 17 Iraqi civilians, lawyers in the case and government officials briefed on the matter said Monday.

The opening of the grand jury inquiry is significant because it indicates that prosecutors believe there is enough evidence of wrongdoing to warrant a formal criminal investigation.

Officials cautioned that the decision to begin a grand jury inquiry did not mean that prosecutors had decided to charge anyone with a crime in what they said was a legally complex case. Some government lawyers have expressed misgivings about whether a federal law exists that would apply to the actions that employees of N.C.-based Blackwater are accused of committing.

The officials, who spoke on the condition of anonymity because they were discussing grand jury matters, said the subpoenas were mainly to Blackwater employees who were at the scene of the shooting but did not fire their weapons. The prosecutors are also seeking company records compiled at the time of the shooting as well as employee work histories and military service files.

The grand jury inquiry in Washington was first reported Monday by ABC News on the network's Web site. The Washington Post also reported that subpoenas were issued.

Blackwater's spokeswoman, Anne E. Tyrrell, said she could not confirm that a grand jury investigation was under way. She did say that it would not be unexpected that federal prosecutors would convene a grand jury to support the FBI investigation.

"It should come as no surprise that this might happen when the FBI is investigating such a matter," she said.

She added, "If official findings conclude that someone was complicit in wrongdoing, we will support holding that person accountable."