KABUL, Afghanistan — For years, American officials have struggled to curb Afghanistan’s opium industry, rewriting strategy every few seasons and pouring in more than $6 billion over the past decade to combat the poppies that help finance the insurgency and fuel corruption.


It is a measure of the problem’s complexity that officials can find little comfort even in the news this month that blight and bad weather are slashing this year’s poppy harvest in the south. They know from past seasons that blight years lead to skyrocketing opium prices and even greater planting efforts to come.


“Now I am desperate, what can I do?” said Mohammed Amin, a poppy farmer in Tirin Kot in Oruzgan Province, who harvested only one kilogram of opium poppy this year compared with 15 last year. “I don’t have any cash now to start another business, and if I grow any other crops, I cannot make a profit.”


The seemingly unbreakable allure of poppy profits — for producers and traffickers, government officials and Taliban commanders alike — has kept fighting opium at the heart of efforts to improve security. It drove Richard C. Holbrooke, later the special envoy to Afghanistan, to write in 2008: “Breaking the narco-state in Afghanistan is essential, or all else will fail.” 


That concern is no less serious today, on the eve of the departure of thousands of American troops. But even as American leaders continue to emphasize the importance of the anti-opium effort, some officials are privately conceding that there is little chance for its large-scale success before the end of the NATO military mission in 2014.


The withdrawal is one worry. As the money from the Western military and civilian aid programs dwindles, the relative importance of opium to the economy is likely only to increase, said Jean-Luc Lemahieu, the director of the United Nations Office on Drugs and Crime in Afghanistan.


“Some money is available through the licit economy, but less than in the past as the Western contracts dry up, and so the importance of the illicit, informal economy will increase: human trafficking, gems, timber and weapons smuggling, and of course narcotics is a huge chunk of it,” he said, adding: “The prognosis post-2014 is not a positive one.”


Opium poppy, much like the coca grown in Colombia and Peru, poses a number of problems because there is so much money to be made that powerful political players, from police chiefs to governors, inevitably want a cut. The Taliban also support the drug trade, directly by protecting opium farmers, and indirectly by shielding traffickers, who pay off everybody in order to move their products quickly to the borders, according to narcotics experts at the United Nations and the Afghan government.


“Drugs are not the only priority issue for Afghanistan,” said William R. Brownfield, the State Department’s assistant secretary for international narcotics and law enforcement, in an interview this month. “But by the same token, if you do not address the drug issue you will not succeed in the other security, stability, democracy, prosperity objectives you are aiming for.”


Despite all the effort, there are many troubling indicators. Nationwide, the number of poppy-free provinces, which reached a high of 20 in 2010, has now dropped to at least 17 and could be found to be still lower once researchers finish surveying remote provinces. Overall acres under poppy cultivation began rising again in 2009 after a significant drop the year before, and the total has grown slowly but steadily since.


Interdiction, while somewhat improved under new Afghan counternarcotics leadership, nets only about 3.5 percent of the 375 tons of heroin that leaves the country every year, according to the United Nations.


Even the success stories are unlikely to be sustainable, officials say. The prime example is the combined American and British counternarcotics campaign in the Helmand River Valley, in the heart of the province that produces nearly half of Afghanistan’s opium. Since its start in 2009, the military mission has coincided with a 33 percent decrease in opium poppy cultivation in the area, and concurrent programs to create alternative jobs and crops have had a significant effect there.