Only 28 percent of Americans say the war in Afghanistan has been worth fighting, the lowest number on record and clearly below the least-popular stretches of the Iraq war, according to a new Washington Post-ABC News poll.

Overall support for U.S. military operations in Afghanistan has dropped 11 percentage points since March, a precipitous fall during a period marked by tension between U.S. officials and Afghan President Hamid Karzai, a spring and summer resurgence in Taliban attacks, and the failure of ballyhooed peace talks with insurgents to get off the ground.

The drop in approval was matched by an 11-point increase, to 67 percent, in those who say the war has not been worth fighting.

The numbers come as Congress has moved to cut President Obama’s budget request for operations in Afghanistan, and the administration is reportedly leaving open the possibility of withdrawing all troops by the end of next year, when combat forces are scheduled to pull out.

Declining support crosses demographic and party lines, with double-digit drops among men and women, whites and non-whites, Democrats, Republicans and independents.

Americans sour on Afghan war

While Republicans generally remain more supportive than Democrats, their approval has collapsed at a faster rate in recent years.

Fewer than half of Americans — 43 percent — say that the Afghan war has contributed to long-term U.S. security, the first time that number has dipped below 50 percent in the past four years. While a majority of Republicans — 55 percent — see the war’s contribution more favorably than other political groups, the current number is down considerably from 70 percent in 2010.

The poll was conducted July 18 to 21 among a random national sample of 1,002 adults. Results from the full poll have an error margin of 3.5 percentage points.

Support for the war was extraordinarily high at its inception, with more than 90 percent saying they supported the U.S.-led effort through early 2002. But a smaller, 56 percent majority said the war was worth fighting in early 2007, when The Washington Post and NBC News first asked the question, just after President George W. Bush announced an additional deployment of 3,200 troops, bringing the total to about 26,000.

That high point of approval was reached again in March 2009, after Obama, two months into his first term, announced a 50 percent increase in the number of deployed troops, bringing the total in Afghanistan to about 53,000.

Although the size of the force continued to increase, eventually reaching about 100,000, support for the war began to slide in 2010 — a year marked by the highest number of U.S. military deaths, the firing of the U.S. commander, Gen. Stanley A. McChrystal, and the publication of classified documents about Afghanistan by WikiLeaks — and never recovered. By mid-July, total U.S. casualties in the war reached 2,248 dead and more than 19,000 wounded, according to Pentagon figures.

In June 2011, Obama outlined his plan for troop withdrawal, and U.S. forces today number about 68,000, and they have moved into a support role for the Afghan army. Half of those are to be withdrawn by next spring, with the remainder leaving by the end of December 2014.

Slightly more than half — 53 percent — of those questioned in the poll said that most, but not all, U.S. troops should leave Afghanistan in the coming year, while 43 percent said all of them should be removed.

Obama has said he wants to leave a residual force there to assist and advise Afghan forces and to continue counterterrorism operations against al-Qaeda. The size and the mission of a post-2014 force is still under discussion in Washington and the subject of negotiations with Karzai’s government.

Senior U.S. military officials have suggested that the residual force should number about 10,000 to 12,000, although larger numbers have been proposed, and some administration officials would like to see it as small as 5,000. Talks that began with the Afghan government last year have been bumpy, with Karzai first stopping the formal negotiations until the United States fulfilled a pledge to turn over all of its prison facilities and prisoners in Afghanistan.

Last month, Karzai again suspended the talks to protest an abortive, U.S.-backed attempt to open a Taliban negotiating office in the Persian Gulf country of Qatar. Although formal negotiations have not yet resumed, working groups have continued to discuss the parameters of a deal. But administration officials did not dispute recent news reports that complete withdrawal, or a “zero option,” was on the table.

Meanwhile, amid government and congressional oversight reports of ongoing Afghan corruption and misspent U.S. funds, House and Senate committees considering Obama’s 2014 budget request cut substantial portions of Afghanistan support spending.

Public support for the Iraq war sank to its lowest point — 33 percent — in November 2011, just a month before the final U.S. troop withdrawal.

Clement is a survey research analyst with Capital Insight, the independent polling group of Washington Post Media.