By Monday, the 19-year-old had learned a lesson that is taught to every generation of G.I.: Bravado will get you only so far.

“I feel we’re actually facing a real enemy now,’’ said Gandy, of Adel, Ga., one of a team of forward observers for the 3rd Infantry Division’s 2nd Brigade, Cyclone Company. “Some mortar rounds landing close to your position will make you feel life is fragile.’’

Spread out on a high desert plain on the northernmost part of the front, this armored company awaits with newfound sobriety an almost certain engagement with some of the most hardened and dedicated forces supporting Saddam: the Medina Division of the Republican Guard, three brigades strong, with tanks and advanced equipment that can put up a real fight.

In a stinging taste of the battle that awaits, Iraq sent a column of 30 armored vehicles south toward the Karbala Gap, a key choke point standing between US forces and Baghdad. Air support pushed it back, destroying 10 tanks and a handful of other vehicles, local commanders reported Monday. One US soldier was killed by sniper fire near the company’s present position.

The fighting followed a tense Sunday night during which the company, along with several others from the 4th Battalion, 64th Armored Regiment, were harassed by mortar fire and small bands of lightly armed militia creeping out of Najaf across the broad muddy fields along the Euphrates River.

Several rounds landed within 50 yards of the company’s vehicles, close enough that you could hear the whistle as they approached and exploded with a ground-shaking boom. “The first 48 hours was very motivating, but after last night, it makes you realize how lucky you really are,’’ said Sgt. Luther Robinson, medic to Cyclone Company. The generals insist the war is proceeding according to plan, right on schedule. But after Iraq captured and killed several US soldiers, and after Iraqi forces put up deadly resistance, some of the men on the ground wonder.

Pvt. David Bilicki, a 19-year-old Pittsburgh native who joined up “to get my life started’’ and set the stage for marrying his fiancee, Diane Roberts, now just wants to go home alive. “I’m an idiot. I should’ve been a medic in the Air Force, like my mother,’’ Bilicki said. Instead, he zips around the desert in a lightly armored vehicle spotting the enemy and calling for fire at the leading edge of the company.

“If I walk out of this, it’ll be a good experience to talk about,’’ Bilicki said. “They were positive we wouldn’t have contact (with enemy forces) until Karbala. We had contact all the way up, as it turns out. You saw burned-out vehicles the whole way.’’

As a result, the predicted pace of this assault has slowed. Cyclone company and the whole 2nd Brigade was stopped short of the Karbala Gap on Monday as other elements of the brigade fought to secure key river crossings east of here.