(Massoud Hossaini/AP Photo)

Fewer than four in 10 Americans say the war in Afghanistan was worth fighting - up from its low but still a broadly negative judgment on the United States' longest conflict.

Asked to consider its costs vs. benefits, 38 percent in this ABC News/Washington Post poll say the war in Afghanistan was worth fighting; 56 percent say it was not. While still a negative view, that's eased from 28-67 percent in July 2013, as U.S. forces gradually have disengaged.

Americans divide essentially evenly on whether the conflict achieved its aim of improving long-term U.S. security, 48-47 percent. But only 19 percent say it contributed "a great deal" to the security of the United States, a key reason most say it wasn't worth fighting.

Despite these attitudes, the survey, produced for ABC by Langer Research Associates, finds majority support for plans to keep up to 10,000 U.S. forces in Afghanistan "to train Afghan forces and assist in counter-insurgency operations" in the year ahead: Fifty-four percent are in favor, though a substantial 43 percent are opposed.

The United States and its NATO allies officially ended their combat role in Afghanistan last week, 13 years after the U.S.-led invasion ousted the Taliban government in response to its support for the al Qaeda terrorist network. More than 2,200 U.S. soldiers were killed, as were more than 1,000 from allied nations and thousands of Afghan civilians.

The invasion initially enjoyed broad U.S. public support, but that ebbed as the conflict dragged on. A majority hasn't called the war worth fighting since 2009.

Assessments of whether the war improved U.S. security are central to views of whether it was worth the effort. Among the two in 10 Americans who say it bolstered security a great deal, 76 percent also say the war was worth fighting. Among those who see more modest security gains, fewer, but still 56 percent, say the same. Among the half who don't think it improved long-term security, by contrast, only 13 percent say the war was worth fighting, 85 percent not.

There also are strong political and ideological components to these views. Republicans and conservatives - particularly those who say they're very conservative - are far more likely than independents, Democrats, moderates or liberals to see the war as worth fighting. That said, even among Republicans, just 23 percent say the war contributed a great deal to U.S. security.

METHODOLOGY - This ABC News/Washington Post poll was conducted by telephone Dec. 11-14, 2014, in English and Spanish, among a random national sample of 1,000 adults, including landline and cell-phone-only respondents. Results have a margin of sampling error of 3.5 points, including design effect.

The survey was produced for ABC News by Langer Research Associates of New York, N.Y., with sampling, data collection and tabulation by Abt-SRBI of New York, N.Y.