KABUL, Afghanistan — The effort to win over Afghans on former Taliban turf in Marja has put American and NATO commanders in the unusual position of arguing against opium eradication, pitting them against some Afghan officials who are pushing to destroy the harvest.

From Gen. Stanley A. McChrystal on down, the military’s position is clear: “U.S. forces no longer eradicate,” as one NATO official put it. Opium is the main livelihood of 60 to 70 percent of the farmers in Marja, which was seized from Taliban rebels in a major offensive last month. American Marines occupying the area are under orders to leave the farmers’ fields alone.

“Marja is a special case right now,” said Cmdr. Jeffrey Eggers, a member of the general’s Strategic Advisory Group, his top advisory body. “We don’t trample the livelihood of those we’re trying to win over.”

United Nations drug officials agree with the Americans, though they acknowledge the conundrum. Pictures of NATO and other allied soldiers “walking next to the opium fields won’t go well with domestic audiences, but the approach of postponing eradicating in this particular case is a sensible one,” said Jean-Luc Lemahieu, who is in charge of the United Nations Office on Drugs and Crime here.