MARJA, Afghanistan — Thousands of Afghan migrant workers expected here in the next few weeks for the spring opium harvest will find at least as much work as last year.

A multimillion-dollar U.S. program that was started last fall to persuade farmers to plant wheat instead of opium poppies did not make a dent in the amount of cultivation in Helmand province, the heart of Afghanistan’s poppy region, according to a recent U.N. survey. U.S. Marines, who arrived here in force seven weeks ago to wrest control of the province from the Taliban, are under orders to win over the population and leave their poppy fields alone.

“You may have landed in one of the only wheat fields in Helmand,” Brig. Gen. Lawrence Nicholson, the Marine commander here, said last week as he greeted a visiting Adm. Mike Mullen, chairman of the Joint Chiefs of Staff. Mullen’s V-22 Osprey set down amid soft, foot-high green shoots beside the headquarters of the Marja district governor for a meeting with local leaders.

Beyond the wheat, pink poppies were blooming in every direction.

The Obama administration decided last year to stop alienating Afghan farmers by eradicating poppy fields and to concentrate instead on arresting drug lords and interdicting drug shipments on their way across and out of the country. At planting time last fall, impoverished residents in accessible areas of Helmand were offered seeds, fertilizer and agricultural assistance to grow alternative crops, primarily wheat.

But the program, hampered by security concerns and the slow arrival of U.S. civilian specialists, barely got started. For many Afghan farmers, even those with access to the substitution program, the decision was a simple one. The market price of wheat dropped nearly 40 percent last year, compared with 6 percent for harvested, dry opium, according to U.N. figures.

The projected stability in this year’s crop stops a dramatic decrease from 2008, a bumper year for opium, to 2009, when cultivation dropped by 22 percent, and by more than one-third in Helmand. Last year, 20 of Afghanistan’s 34 provinces were declared poppy-free.

According to the United Nations’ annual winter cultivation survey compiled in February, however, that number has dropped to 17 for 2010, with new growth in three northern provinces previously said to be poppy-free. “Modest increases” were noted in four other provinces. In Helmand, where half of Afghanistan’s poppy is grown, cultivation has remained “stable” since 2009, the United Nations said.

Today, as the Marines slowly expand their tenuous hold on territory in and around the Marja district, the last petals and leaves are falling from the plants. In a few weeks, only next year’s seed capsules will remain, ready for harvest.

Opium harvesting is labor-intensive and some of the highest paying agricultural work in Afghanistan. Migrants come from throughout the country, some from across the southern border with Pakistan, to score the capsules with sharp knives, allow the gummy opium to ooze out, and collect it as it dries.

Nicholson said his plan for limiting the spring yield is to block main roads into the area and turn back migrants.

Processing opium that farmers do manage to harvest will be limited, he said, because the U.S. military and Drug Enforcement Administration, along with Afghan security forces, have prevented the shipment into Afghanistan of production chemicals.

According to the DEA, which has 96 agents in Afghanistan, seizures of processed opium increased by 924 percent last year, because of increased cooperation between Afghan and foreign forces here.

Afghans who see their anticipated income disappearing for the year, Nicholson said, will be offered the $5 daily stipend the Americans here pay for clearing rubble and irrigation ditches. Migrants who are turned away will have to seek work elsewhere.

There is disagreement in the U.S. government about how much income the Taliban derives from the drug trade. Some intelligence and drug enforcement officials think it is a major source of insurgent revenue from taxes levied on farmers as well as trafficking of processed narcotics.

But Richard Holbrooke, the Obama administration’s special representative for Afghanistan and Pakistan, has consistently said that it is at best a minor source of insurgent revenue.

“Eradication is a waste of money,” Holbrooke said last summer in outlining the end of the Bush administration’s focus on destroying poppies. “The farmers are not our enemy, they’re just growing a crop to make a living.” Previous policy, he said, “was driving people into the hands of the Taliban.” The administration would focus instead on interdicting traffickers and substituting crops.

Not everyone has been pleased by the end of the eradication program.

Russia appealed to NATO last month to return to crop destruction, arguing that Afghan opium was killing up to 30,000 Russians each year.

The request was rejected, and NATO spokesman James Appathurai told reporters in Brussels that neither the international coalition in Afghanistan nor the Afghan government thought eradication was desirable.

NATO Secretary General Anders Fogh Rasmussen, Appathurai said, had told top Russian anti-drug official Viktor Ivanov that Russia should join the international effort to improve Afghan counternarcotics training and also supply badly needed helicopters for the overall counterinsurgency effort.

That, he said, “is the most effective way to tackle the drug problem.”

Said Appathurai: “We cannot be in a situation where we remove the only source of income of people who live in the second-poorest country in the world without being able to provide them with an alternative.”