FORWARD OPERATING BASE SHANK, Afghanistan — Veterans of Iraq recall rolling to war along asphalted highways, sweltering in flat scrublands and chatting with city-wise university graduates connected to the wider world.

Now fighting in Afghanistan, U.S. soldiers invariably encounter illiterate farmers who may never have talked to an American as they slog into remote villages on dirt tracks through bitterly cold, snow-streaked mountains.

"Before deploying here we were given training on language, culture, everything. I thought that since I was an Iraq combat veteran, I didn't need any of that stuff. I was wrong. Both countries may be Muslim but this is a totally different place," says Sgt. Michael McCann, returning from a patrol in the east-central province of Logar.

As they await details of President Barack Obama's strategy for Afghanistan in a national address Tuesday, soldiers in the field say no one should look at Afghanistan and Iraq as similar combat zones.

Soldiers and officers involved in combat operations all cite the more punishing geography and climate, those focused on development the bare-bones infrastructure, and intelligence specialists the even greater difficulties in identifying the insurgents as among the many sharp contrasts between Afghanistan and Iraq.

"The sheer terrain of Afghanistan is much more challenging: the mountains, the altitudes, severity of weather, the distances. That wears on an army," says Maj. Joseph Matthews, a battalion operations officer in the 10th Mountain Division. "You can flood Baghdad with soldiers but if you want to flood the mountains you are going to need huge numbers and logistics."

McCann, a military policeman from Enterprise, Ala., says that the highest he ever got during his Iraq tour was a five-story building. In Afghanistan, troops routinely cross passes 10,000 feet and higher, descending into valleys where they say villagers "hibernate like bears" for up to five winter months, cut off from the outside world by the snows.

This almost medieval isolation makes it far more difficult for the Afghan government and coalition forces to spread the aid and information needed to counter the Taliban push while the villagers — mostly illiterate and with little access to radios, never mind television — rely on religious leaders at Friday mosque prayers, or the insurgents, to shape their world view.

"When you have a society that can't read for itself and religious leaders are trusted, they can say whatever they like and people will believe them. It's hard for the U.S. to penetrate and influence this. In Iraq there are other ways to get the message across," says Chief Warrant Officer Daniel Weiermann Jr., an intelligence specialist.

While counterinsurgency in Iraq had its unique complexities, Weiermann said that in Iraq — about 70 percent urbanized as opposed to 25 percent in Afghanistan — "you can meet and hopefully influence a lot of people in one day. In Afghanistan, with its great distances, sparsely populated areas and rugged terrain you can do far less in the same amount of time."

Development — which absorbs the U.S. military more than combat and is regarded as key to victory — is also far tougher than in Iraq, which already possessed a solid infrastructure.

In Afghanistan at best a quarter of the population can read, compared to more than 75 percent in Iraq, which had functioning banking, medical and other systems, however imperfect, through which aid could be channeled.

"Iraq already had the foundation. They just needed the governance piece that would support not just the elite few. In Afghanistan, you are starting at the very beginning. It's like trying to take the American Indians in their purest form and put them into today's New York City. It's not going to happen," says Weiermann, of Fort Hood, Texas.

The countries do have one thing in common. Pinpointing the insurgents has been devilishly difficult in both countries.

"Osama bin Laden could walk right up to me and I wouldn't have a clue to who he was. The enemy cannot be identified at first sight. The enemy blends in easily with the population. That is the same for both places but drastically harder in Afghanistan," Weiermann says.