WASHINGTON — Five former Blackwater Worldwide security guards pleaded not guilty Tuesday to federal manslaughter and gun charges resulting from a 2007 shooting in a crowded Baghdad square that killed 17 Iraqi civilians and injured dozens of others.

The five — all decorated military veterans — stood silently in a line behind their lawyers as their not guilty plea on all charges was entered in front of U.S. District Judge Ricardo M. Urbina in federal court.

They are charged with 14 counts of manslaughter, 20 counts of attempted manslaughter and one count of using a machine gun to commit a crime of violence. The machine gun charge, typically used in drug cases, carries a 30-year minimum prison sentence.

Saying the case was complex, Urbina set a February 1, 2010 hearing date for former Marines Donald Ball of West Valley City, Utah; Dustin Heard of Knoxville, Tenn.; Evan Liberty of Rochester, N.H.; and Army veterans Nick Slatten of Sparta, Tenn., and Paul Slough of Keller, Texas.

The Iraqi government has labeled the guards "criminals" and is closely watching the Blackwater case. The shooting strained diplomacy between Washington and Baghdad and fueled the anti-American insurgency in Iraq, where many Iraqis saw the bloodshed in Nisoor Square as a demonstration of American brutality and arrogance.

The shooting took place around noon on Sept. 16, 2007, in a crowded square where prosecutors said civilians were running errands, getting lunch and otherwise going about their lives.

Prosecutors said the men unleashed a gruesome attack on unarmed Iraqis, with the slain including young children, women, people fleeing in cars and a man whose arms were raised in surrender as he was shot in the chest.

Twenty others were wounded in the crowded square, including one injured by a grenade launched into a nearby girls' school. Another 18 Iraqis were assaulted but not wounded, prosecutors said.

Iraqi witnesses said the contractors opened fire unprovoked and left the square littered with blown-out cars.

"This is a straightforward shooting of a lot of people," Assistant U.S. Attorney Kenneth C. Kohl said.

But the Blackwater guards contend they were ambushed by insurgents. One of the trucks in the convoy was disabled in the ensuing firefight, the guards say.

Blackwater radio logs made available to The Associated Press by a defense attorney in the case last month raised questions about prosecutors' claims that the guards' shooting was unprovoked. The log transcripts describe a hectic eight minutes in which the guards repeatedly reported incoming gunfire from insurgents and Iraqi police.