WASHINGTON — A draft report by American intelligence agencies concludes that Afghanistan is in a “downward spiral” and casts serious doubt on the ability of the Afghan government to stem the rise in the Taliban’s influence there, according to American officials familiar with the document.

The classified report finds that the breakdown in central authority in Afghanistan has been accelerated by rampant corruption within the government of President Hamid Karzai and by an increase in violence by militants who have launched increasingly sophisticated attacks from havens in Pakistan.

The report, a nearly completed version of a National Intelligence Estimate, is set to be finished after the November elections and will be the most comprehensive American assessment in years on the situation in Afghanistan. Its conclusions represent a harsh verdict on decision-making in the Bush administration, which in the months after the Sept. 11, 2001, attacks made Afghanistan the central focus of a global campaign against terrorism.

Beyond the cross-border attacks launched by militants in neighboring Pakistan, the intelligence report asserts that many of Afghanistan’s most vexing problems are of the country’s own making, the officials said.

The report cites gains in the building of Afghanistan’s national army, the officials said. But they said it also laid out in stark terms what it described as the destabilizing impact of the booming heroin trade, which by some estimates accounts for 50 percent of Afghanistan’s economy.

The Bush administration has initiated a major review of its Afghanistan policy and has decided to send additional troops to the country. The downward slide in the security situation in Afghanistan has also become an issue in the presidential campaign, along with questions about whether the White House emphasis in recent years on the war in Iraq has been misplaced.

Inside the government, reports issued by the Central Intelligence Agency for more than two years have chronicled the worsening violence and rampant corruption inside Afghanistan, and some in the agency say they believe that it has taken the White House too long to respond to the warnings.

Henry A. Crumpton, a career C.I.A. officer who last year stepped down as the State Department’s top counterterrorism official, attributed some of Afghanistan’s problems to a “lack of leadership” both at the White House and in European capitals where commitments to rebuild Afghanistan after 2001 have never been met.

Mr. Crumpton, who was in charge of the C.I.A. teams that entered Afghanistan after the 9/11 attacks but who said he had not seen the draft report, said that Afghanistan was “bad and getting worse” and that officials in Washington were just beginning to wake up to the problem.

“It’s taken them a long time to realize it, but now they know it’s pretty grim,” he said.

A National Intelligence Estimate is a formal document that reflects the consensus judgments of all 16 American intelligence agencies. Although the Bush administration has made public the crucial findings from some recent N.I.E.’s on Iraq and terrorism, most remain classified. The assessment on Afghanistan is the first since the Taliban regained strength there beginning in 2006 and launched an offensive that has allowed them to seize large swaths of territory.

The draft intelligence report was described by more than a half dozen current government officials who had read its conclusions. They spoke on the condition of anonymity because the report remains classified and has not been completed.

Richard Willing, a spokesman for the Office of the Director of National Intelligence, which produces the national intelligence assessments, declined to comment for this article. A White House spokesman, Gordon D. Johndroe, also declined to comment on the report’s conclusions but said: “Everyone understands that the current situation in Afghanistan is a tough one. That’s why the president ordered additional troops there. That’s why we’re increasing the size of the Afghanistan Army.”

Both major presidential candidates, Senators Barack Obama and John McCain, have called for American troop increases in Afghanistan even beyond those the White House has ordered. Mr. Obama has accused the White House of paying too little attention to Afghanistan as it poured the vast bulk of American military resources into the war in Iraq, while Mr. McCain has defended the administration’s decision, saying that Iraq remains the more important front in the battle against terrorism.

In Tuesday’s presidential debate, Mr. Obama said he told Mr. Karzai during a visit to Afghanistan in July that the Afghan leader had “to do better by your people in order for us to gain the popular support that’s necessary.”

“We have to have a government that is responsive to the Afghan people, and frankly it’s just not responsive right now,” Mr. Obama said.

American officials said that intelligence agencies were also working to produce an assessment on Pakistan, and that both were to be completed after next month’s elections. They said the draft findings had already begun to influence the recommendations of the White House-led review of Afghanistan policy, which was scheduled to be completed this month but has now been postponed several weeks.

The administration is considering whether the United States should devote more effort to working directly with tribal leaders in far-flung provinces, and possibly arming tribal militias, to fight the Taliban in places where Afghanistan’s army and police forces have been ineffective.

The Bush administration had long resisted making tribal elders a centerpiece of American strategy in Afghanistan. American officials had hoped instead that strong national institutions like the Afghan Army could protect the Afghan population, but the escalating violence this year has forced a reassessment of the value of the tribal system for counterinsurgency operations.

“In order to have an effective counterinsurgency strategy, you need to have strong local governance in the districts and the provinces,” said a senior State Department official who has been briefed on the report’s broad conclusions, and who spoke on the condition of anonymity.

In a sign of the seriousness of the administration’s policy review, the White House’s top coordinator for Afghanistan policy, Lt. Gen. Douglas E. Lute of the Army, will lead a team of specialists who will go there to assess the situation, a senior administration official said Wednesday.

Administration officials say the review is examining how and where the nearly $6 billion in annual American assistance to Afghanistan is being spent; how to improve the effectiveness of small teams of American and European civilians and troops seeded throughout the Afghan provinces to spur economic growth; and how to strike the right balance between taking military action against the Taliban and Al Qaeda in Pakistan and providing more development aid to that country.

Senior American commanders have recently been blunt in their assessment of the security trends in the country. “In large parts of Afghanistan, we don’t see progress,” Gen. David D. McKiernan, the top American officer in Afghanistan, told reporters last week. “We’re into a very tough counterinsurgency fight and will be for some time.”

It is not just American officials who offer a grim prognosis. A French diplomatic cable leaked to a French newspaper last week quoted the British ambassador to Afghanistan as forecasting that the NATO-led mission there would fail.

“The current situation is bad, the security situation is getting worse, so is corruption, and the government has lost all trust,” the British envoy, Sherard Cowper-Coles, was quoted as telling the French deputy ambassador to Kabul, who wrote the cable.

British officials have said the comments attributed to Sir Sherard were distorted and do not reflect official British policy.