United States officials warned this month in an internal memo that an American-financed poppy eradication program aimed at curtailing Afghanistan's huge heroin trade had been ineffective.  A copy of the three-page cable, which was addressed to Secretary of State Condoleezza Rice, was shown to The New York Times by an American official alarmed at the slow pace of poppy eradication.

The cable faulted Britain, which has the top responsibility for counternarcotics assistance in Afghanistan, for being "substantially responsible" for the failure to eradicate more acreage. British personnel choose where the eradication teams work, but the cable said that those areas were often not the main growing areas and that the British had been unwilling to revise targets.

There is moutning frustration among some American officials that plans to uproot large swaths of Afghanistan's poppy crop have produced little success. These officials said they worried that heroin trafficking could threaten the American-led reconstruction effort in Afghanistan and worsen corruption in the country's fledgling central government.

In Washington, State Department officials defended Afghanistan President Hamid Karzai, who is scheduled to visit next week, saying the effort had been hampered by bad weather and logistical problems as well as by political resistance.

"President Karzai is a strong partner and we have confidence in him," said the State Department spokesman, Richard A. Boucher. "We are succeeding in our overall effort" to address the drug problem.

American and Afghan officials decided late last year that a more aggressive anti-poppy effort was too risky. State Department officials had proposed aerial spraying of poppy-growing areas, but the plan was opposed by Ambassador Zalmay Khalilzad and American military officials in Afghanistan who agreed, though effective at killing poppies, spraying fields by aircraft could lead to protests and unrest.

A spokeswoman for the British Foreign Office defended the choice of targets. "We don't believe we are picking the wrong targets, but we have a long struggle to go," she said. "We work very closely with the U.S. and other partners."

The spokeswoman said that eradication only worked if there were alternatives in place for the poppy growers, and that is where Britain is placing most of its emphasis.

A major reason Britain was put in charge of counternarcotics efforts is that much of the heroin produced from Afghan poppies ends up in European countries - roughly 50 tons a year, compared to the 20 tons estimated to go to the United States.

Since beginning work last month, the country's Central Poppy Eradication Force, an American-trained group, has destroyed less than 250 acres, according to the two American officials. Its original goal was to eradicate 37,000 acres, but that target has recently been reduced to 17,000 acres. With the poppy harvest already under way, the actual eradication levels will probably be far lower, the American officials said.

The department's annual drug-trafficking report, released in March, warned that Afghanistan was "on the verge of becoming a narcotics state."

American officials have said publicly that Mr. Karzai recognized the severity of the poppy cultivation problem and was determined to combat it, albeit gradually, to avoid inciting unrest among Afghans whose incomes are dependent on growing poppies for the drug trade. Congress recently passed a supplemental spending bill that included $260 million for the State Department's anti-drug effort in Afghanistan this year.

A senior State Department official said that Mr. Karzai had wanted the eradication team to begin work before the poppy harvest season began in March, when he felt there was a better chance of persuading farmers to give up that lucrative crop. But because of bad weather and other delays the team did not begin work until early April.

The American officials involved said they also believed that Mr. Karzai might not want to challenge local Afghan authorities and thus incite opposition and even violence ahead of parliamentary elections scheduled for next fall.

The eradication effort got under way last month in the southern province of Kandahar and in neighboring Helmand and has now shifted to the Balkh Province in the north.

In Kandahar Province this week, farmers were scraping the last resin from poppy plants, in plain view of the main road, just 10 minutes outside the provincial capital, once a stronghold of the Taliban.

"Karzai's order will only be acceptable when he sends money to the farmers and helps them," said a poppy farmer, Jan Agha. After investing in water, fertilizer and labor, farmers would resist eradication, he said, adding, "In the villages people would fight."

A State Department official said that the United States remained optimistic that, through a combination of eradication and reduced plantings, it could achieve a 70,000-acre reduction in poppy planting from last year's record crop, which was estimated at more than 500,000 acres.

Because of the faltering eradication effort, much of the acreage reduction the Americans hope for is likely to be from farmers deciding not to plant, the officials conceded. And even if that goal is reached, the crop may still be the second largest ever, a senior American official said.

Mr. Karzai called for a "jihad" against drugs after his election last November, Mr. Ludin pointed out. But he also noted that Mr. Karzai would risk losing his moral authority if promised assistance to the poppy farmers was not forthcoming.

"It is actually the international community that is showing a lack of seriousness, by failing to show that there is an alternative for farmers," he said.

On their first day of operations in early April, in the Maiwand district of Kandahar Province, the eradication force encountered armed farmers blocking the fields. Gunfire broke out, resulting in the death of at least one Afghan protester and the wounding of several others.

The American officials said they suspected the protesters had been organized by traffickers and local officials with a stake in the drug trade.

Over the next eight days, according to the embassy cable, American and British officials in Kabul sought help from the Afghan minister responsible for the anti-drug effort, Habibullah Qaderi, to end the confrontation in Maiwand and a similar standoff in nearby Panjwayi. But he was unable to persuade the Kandahar authorities to help, the embassy cable said. Mr. Qaderi could not be reached for comment.

The embassy cable praised Muhammad Daoud, the deputy minister of the interior for the anti-drug effort, for trying to win access for the eradication teams, but it said he had "no support whatsoever from key members" of the government, "namely President Karzai."

When the eradication unit did begin work, it was permitted to destroy only limited amounts of poppies in fields designated by local officials, the cable said, which were widely scattered. On most days, only 40 to 100 workers showed up to help, not the 300 to 400 promised by the local leaders, the cable said.