The Marines of Bravo Company's 1st Platoon sleep beside a grove of poppies. Troops in the 2nd Platoon playfully swat at the heavy opium bulbs while walking through the fields. Afghan laborers scraping the plant's gooey resin smile and wave.

Last week, the 24th Marine Expeditionary Unit moved into southern Helmand province, the world's largest opium poppy-growing region, and now find themselves surrounded by green fields of the illegal plants that produce the main ingredient of heroin.

The Taliban, whose fighters are exchanging daily fire with the Marines in Garmser, derives up to $100 million a year from the poppy harvest by taxing farmers and charging safe passage fees - money that will buy weapons for use against U.S., NATO and Afghan troops.

Yet the Marines are not destroying the plants. In fact, they are reassuring villagers the poppies won't be touched. American commanders say the Marines would only alienate people and drive them to take up arms if they eliminated the impoverished Afghans' only source of income.

Many Marines in the field are scratching their heads over the situation.

"It's kind of weird. We're coming over here to fight the Taliban. We see this. We know it's bad. But at the same time we know it's the only way locals can make money," said 1st Lt. Adam Lynch, 27, of Barnstable, Mass.

The Marines' battalion commander, Lt. Col. Anthony Henderson, said in an interview Tuesday that the poppy crop "will come and go" and that his troops can't focus on it when Taliban fighters around Garmser are "terrorizing the people."

"I think by focusing on the Taliban, the poppies will go away," said Henderson, a 41-year-old from Washington, D.C. He said once the militant fighters are forced out, the Afghan government can move in and offer alternatives.

An expert on Afghanistan's drug trade, Barnett Rubin, complained that the Marines are being put in such a situation by a "one-dimensional" military policy that fails to integrate political and economic considerations into long-range planning.

"All we hear is, not enough troops, send more troops," said Rubin, a professor at New York University. "Then you send in troops with no capacity for assistance, no capacity for development, no capacity for aid, no capacity for governance."

Most of the 33,000 U.S. troops in Afghanistan operate in the east, where the poppy problem is not as great. But the 2,400-strong 24th Marines, have taken the field in this southern growing region during harvest season.

In the poppy fields 100 feet from the 2nd Platoon's headquarters, three Afghan brothers scraped opium resin over the weekend. The youngest, 23-year-old Sardar, said his family would earn little money from the harvest.

"We receive money from the shopkeepers, then they will sell it," said Sardar, who was afraid to give his last name. "We don't have enough money to buy flour for our families. The smugglers make the money," added Sardar, who worked alongside his 11-year-old son just 20 yards from a Marine guard post, its guns pointed across the field.

Afghanistan supplies some 93 percent of the world's opium used to make heroin, and the Taliban militants earn up to $100 million from the drug trade, the United Nations estimates. The export value of this harvest was $4 billion - more than a third of the country's combined gross domestic product.

Though they aren't eradicating poppies, the Marines presence could still have a positive effect. Henderson said the drug supply lines have been disrupted at a crucial point in the harvest. And Marine commanders are debating staying in Garmser longer than originally planned.

Second Lt. Mark Greenlief, 24, a Monmouth, Ill., native who commands the 2nd Platoon, said he originally wanted to make a helicopter landing zone in Sardar's field. "But as you can see that would ruin their poppy field, and we didn't want to ruin their livelihood."

Sardar "basically said, 'This is my livelihood, I have to do what I can to protect that,'" said Greenlief. "I told him we're not here to eradicate."

The Taliban told Garmser residents that the Marines were moving in to eradicate, hoping to encourage the villagers to rise up against the Americans, said 2nd Lt. Brandon Barrett, 25, of Marion, Ind., commander of the 1st Platoon.

In the next field over from Sardar's, Khan Mohammad, an Afghan born in Helmand province who lives in Pakistan and came to work the fields, said he makes only $2 a day. He said the work is dangerous now that Taliban militants are shooting at the U.S. positions.

"We're stuck in the middle," he said. "If we go over there those guys will fire at us. If we come here, we're in danger, too, but we have to work," said the 54-year-old Mohammad, who supports a family of 10.

An even older laborer, his back bent by years of work, came over and told the small gathering of Afghans, Marines and journalists that the laborers had to get back to work "or the boss will get mad at us."

Staff Sgt. Jeremy Stover, whose platoon is sleeping beside a poppy crop planted in the interior courtyard of a mud-walled compound, said the Marines' mission is to get rid of the "bad guys," and "the locals aren't the bad guys."

"Poppy fields in Afghanistan are the cornfields of Ohio," said Stover, 28, of Marion, Ohio. "When we got here they were asking us if it's OK to harvest poppy and we said, 'Yeah, just don't use an AK-47.'"