WASHINGTON — After a series of violent episodes and setbacks, support for the war in Afghanistan has dropped sharply among both Republicans and Democrats, according to the latest New York Times/CBS News poll. Haraz N. Ghanbari/Associated Press Gen. John R. Allen said on Monday that insurgents would continue to try to “disrupt the integrity” of Afghan security forces. The New York Times The survey found that more than two-thirds of those polled — 69 percent — thought that the United States should not be at war in Afghanistan. Just four months ago, 53 percent said that Americans should no longer be fighting in the conflict, more than a decade old. The increased disillusionment was even more pronounced when respondents were asked their impressions of how the war was going. The poll found that 68 percent thought the fighting was going “somewhat badly” or “very badly,” compared with 42 percent who had those impressions in November. The latest poll was conducted by telephone from March 21 to 25 with 986 adults nationwide. It has a margin of sampling error of plus or minus three percentage points. The Times/CBS News poll was consistent with other surveys this month that showed a drop in support for the war. In a Washington Post/ABC News poll, 60 percent of respondents said the war in Afghanistan had not been worth the fighting, while 57 percent in a Pew Research Center poll said that the United States should bring home American troops as soon as possible. In a Gallup/USA Today poll, 50 percent of respondents said the United States should speed up the withdrawal from Afghanistan. Negative impressions of the war have grown among Republicans as well as Democrats, according to the Times/CBS News poll. Among Republicans, 60 percent said the war was going somewhat or very badly, compared with 40 percent in November. Among Democrats, 68 percent said the war was going somewhat or very badly, compared with 38 percent in November. But the poll found that Republicans were more likely to want to stay in Afghanistan for as long as it would take to stabilize the situation: 3 in 10 said the United States should stay, compared with 2 in 10 independents and 1 in 10 Democrats. Republicans themselves are divided, however, over when to leave, with a plurality, 40 percent, saying the United States should withdraw earlier than the end of 2014, when under an agreement with the Afghan government all American troops are to be out of the country. The poll comes as the White House is weighing options for speeding up troop withdrawals and in the wake of bad news from the battlefield, including accusations that a United States Army staff sergeant killed 17 Afghan civilians and violence set off by the burning last month of Korans by American troops. The poll also follows a number of high-profile killings of American troops by their Afghan partners — a trend that the top American commander in Afghanistan suggested on Monday was likely to continue. “It is a characteristic of this kind of warfare,” Gen. John R. Allen, the commander of NATO forces in Afghanistan, told reporters at a Pentagon news conference. He said that in a counterinsurgency conflict like the one in Afghanistan, where American forces are fighting insurgents while training Afghan security forces, “the enemy’s going to do all that they can to disrupt both the counterinsurgency operation, but also disrupt the integrity of the indigenous forces.” American commanders say that the Taliban have in some cases infiltrated Afghan security forces to attack Americans, but that most cases are a result of personal disputes between Afghans and their American trainers. In follow-up interviews, a number of poll respondents said they were weary after more than a decade of war in Afghanistan, and impatient with the slow progress of Afghan security forces. “I think we should speed up when we’re bringing our troops home,” said Melisa Clemmons, 52, a Republican and a coordinator for a wireless carrier system from Summerville, S.C. “If we’ve been there as many years as we’ve been there, what’s another two years going to get us?” she asked, adding, “These Afghanistan people are turning around and shooting our people. Why is it taking this long for the Afghan troops to be policing themselves?” Paul Fisher, 53, a Republican from Grapevine, Tex., who works in the pharmaceutical business, said the United States should no longer be involved in the war, although he opposed setting a specific timetable. “After a while enough is enough, and we need to get out and move on and let Afghanistan stand on its own merits,” he said. Peter Feaver of Duke University, who has long studied public opinion about war and worked in the administration of President George W. Bush, said that in his view there would be more support for the war if President Obama talked more about it. “He has not expended much political capital in defense of his policy,” Mr. Feaver said. “He doesn’t talk about winning in 2014; he talks about leaving in 2014. In a sense that protects him from an attack from the left, but I would think it has the pernicious effect of softening political support for the existing policy.” The drop in support for the war among Republican poll respondents mirrors reassessments of the war among the party’s presidential candidates, traditionally more hawkish than Democrats. Newt Gingrich declared this month that it was time to leave Afghanistan, while Rick Santorum said that one option would be to withdraw even earlier than the Obama administration’s timeline. Mitt Romney has been more equivocal, although he said last summer that it was “time for us to bring our troops home as soon as we possibly can, as soon as our generals think it’s O.K.” Michael E. O’Hanlon, a military expert at the Brookings Institution who is close to American commanders in Afghanistan, said that the opinion polls reflected a lack of awareness of the current policy, which calls for slowly turning over portions of the country to Afghan security forces, like the southern provinces, where American troops have tamped down the violence. “I honestly believe if more people understood that there is a strategy and intended sequence of events with an end in sight, they would be tolerant,” Mr. O’Hanlon said. “The overall image of this war is of U.S. troops mired in quicksand and getting blown up and arbitrarily waiting until 2014 to come home. Of course you’d be against it.” Among poll respondents, 44 percent said that the United States should withdraw sooner than 2014, while 33 percent said the administration should stick to the current timetable, 17 percent said the United States should stay as long as it would take to stabilize the current situation and 3 percent said the United States should withdraw now.