A four-figure number hovers 50 feet over a busy Philadelphia street, visible in an office window. It changes maybe once or twice a day like the cost of something.

A janitor once stopped, just to stare. "I see that number, and it makes me cry," he told Celeste Zappala, who keeps the running tally.

It is a number that strongly moves American opinion: the U.S. military's death toll in Iraq — 3,000 as of Sunday.

Zappala's son, Sgt. Sherwood Baker, is one of the dead.

Other makeshift memorials rise up across the country as reminders of the war's human cost: flags planted in honor of the dead on the National Mall in Washington, symbolic tombstones at the Liberty Bell in Philadelphia, signs with fallen soldiers' names plastered to telephone poles outside Boston.

Americans may question this war for many reasons, but their doubts often find voice in the count of U.S. war deaths. An overwhelming majority — 84 percent — worry that the war is causing too many casualties, according to a September poll by the nonpartisan research group Public Agenda.

The grim milestone was crossed on the final day of 2006 and at the end of the deadliest month for the American military in Iraq in the past 12 months. At least 111 U.S. service members were reported to have died in December.

The country largely kept the faith during World War II, even as about 400,000 U.S. forces died — 20,000 just in the monthlong Battle of the Bulge. Before turning against the wars in Korea and Vietnam, Americans tolerated thousands more deaths than in Iraq.

Has something changed? Do Americans somehow place higher value on the lives of their soldiers now? Do they expect success at lower cost? Or do most simply dismiss this particular war as the wrong one — hard to understand and harder to win — and so not worth the losses?

The Associated Press recently posed these questions to scholars, veterans, activists and other Americans. Their comments suggest that the public does express more pain over the deaths of this war.

A death toll of 3,000 simply sounds higher to Americans in this war than it did in other prolonged conflicts of the past century for a number of reasons, the interviews suggest.

"As fewer Americans die in war, their loss is more keenly felt, not necessarily at a personal level, but at a collective and public level," says historian Michael Allen at North Carolina State University.

Jeffrey Greenwood, 17, of Plymouth, Mass., though unsure of the exact number of Iraq war deaths, says, "I know it's enough to make people angry."