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In the wake of the biggest opium harvest in Afghanistan’s history, American officials have renewed efforts to persuade the government here to begin spraying herbicide on opium poppies, and they have found some supporters within President Hamid Karzai’s administration, officials of both countries said.

Since early this year, Karzai has repeatedly declared his opposition to spraying the poppy fields, whether by crop-dusting airplanes or by eradication teams on the ground. But Afghan officials said the Karzai administration is re-evaluating that stance.

Many spraying advocates view herbicides as critical to curbing Afghanistan’s poppy crop. That crop and the opium and heroin it produces have become a major source of revenue for the Taliban insurgency.

But officials said the skeptics — who include American military and intelligence officials — fear that spraying American-made chemicals would be a boon to Taliban propagandists. Some said the political cost could be especially high if the herbicide destroys food crops.