The survey - conducted for ABC News, the BBC and the German public TV station ARD - noted that Afghans overwhelmingly prefer the government of President Hamid Karzai to the Taliban, but they also believe that government should negotiate with the Taliban to end the war.
In southwestern Afghanistan, support for NATO-led forces has plummeted to 45 percent this year, from 83 percent a year ago, it found.
"Civilian casualties blamed on these forces is a prime complaint," the survey said.
This year has been the most violent yet since the U.S.-led invasion in 2001, and insurgency-related violence has killed nearly 6,200 people - a record number, according to an AP tally of figures from Afghan and western officials.
More than 800 civilians have died in insurgency attacks and military operations, causing a decline in support for foreign troops and the western-backed government of President Hamid Karzai.
Polltakers conducted 1,377 face-to-face interviews with Afghans in all of the country's 34 provinces. The poll was the third survey in Afghanistan sponsored by ABC News and media partners, and was conducted between Oct. 28 and Nov. 7. It has a three percentage point margin of error.
The survey found that 42 percent of Afghans rate U.S. efforts in Afghan positively, down from 68 percent in 2005 and 57 percent last year.
Just over half of Afghans still have confidence in the ability of U.S. and NATO forces to provide security, down from two-thirds a year ago.
Respondents were particularly critical in the southwestern provinces of Helmand and Kandahar. The former Taliban stronghold and now the biggest opium-producing region in the world has borne the brunt of violence in Afghanistan this year.
"Attitudes are far more negative in high-conflict areas, particularly the southwest provinces of Helmand and Kandahar, but also in western Herat and other areas that have seen Taliban attacks. Views are far more positive in the more peaceful north," the report said.
In the southwest, the birthplace of the Taliban movement and an area of intense combat, two-thirds of Afghans rated U.S. efforts negatively. Twenty-three percent of respondents there said local people support the Taliban - three times more than last year and compared to only 8 percent nationally.
Last year, 81 percent of residents in the southwest said the Taliban had "no significant support at all." Now, only 52 percent say so.
Despite the increasingly negative view of U.S. activities in their country, 71 percent of Afghans still support the American presence, and 76 percent view the Taliban's overthrow as a good thing.
More than a third say the Taliban are the prime cause of violence in the country, followed by 22 percent who blame al-Qaida and foreign fighters. Nineteen percent cite international forces or the U.S. government as the primary cause.
An overwhelming majority of respondents preferred the current government to the Taliban, but 60 percent say Karzai's government should negotiate a settlement in which Taliban leaders would be allowed to hold political office in exchange for laying down their arms.
Karzai said last month that he has had increasing contact with Taliban leaders in exile, but the militant's leaders have ruled out talks as long as foreign troops remain in the country.
The choice of the city of Helsinki is not incidental as the capital of Finland had hosted US-Soviet negotiations on the limitation of nuclear stockpiles in 1969