That warning was underscored on Saturday by a fighter jet crash in eastern Afghanistan that pushed the number of US service members killed in July to 50, making it the deadliest month yet in the eight-year old war.
But in order to reach that long-term goal, he said the US must make clear security gains by next summer or risk losing public support within the United States.
Citing public weariness of the Iraq war, he said the American people are unwilling to get bogged down in another seemingly endless conflict. And if public support for the war wanes, then the "Washington clock" will tick faster and faster toward ending it – whether US goals have been met or not.
"After the Iraq experience, nobody is prepared to have a long slog where it is not apparent we are making headway," Gates said in an interview. "The troops are tired; the American people are pretty tired."
Gates said that Americans would have the patience to continue the war in Afghanistan only if the new military approach began to move the conflict out of deadlock.
"If we can show progress, and we are headed in the right direction, and we are not in a stalemate where we are taking significant casualties, then you can put more time on the Washington clock," he said.
With US casualties in Afghanistan mounting in the run-up to the country's presidential election on August 20, the Pentagon may be in a race against time to bolster public support for the war and counter the idea that its cost is too high.
According to Stars and Stripes, the official US military newspaper, a US F-15E fighter jet crashed in eastern Afghanistan after a mechanical failure at 3:15 am Saturday morning local time. The accident killed two US service members, whose names have yet to be made public.
The nature of the mechanical problem is unclear, but Agence-France Presse reports that hostile fire has been ruled out as a possible cause of the crash. The Taliban are known to lack the ability to shoot down fighter jets , which fly at very high altitudes, despite their success at taking down a number of military helicopters since the start of the war in 2001.
But the title of "deadliest month" has been used a lot lately. The last time analysts talked about the deadliest month of the war was just last month, writes journalist Thomas Ricks on the Foreignpolicy.com blog "Best Defense." In June 2009, 38 coalition soldiers died (27 US, 2 Britain, 2 Canada, 1 Estonia, 3 Denmark, 3 Germany). Roughly 60 percent of them were cut down by roadside bombs.
The Associated Press has prepared a short and sobering – tally of American losses since Operation Enduring Freedom began in response to the World Trade Center attack in 2001. AP says that as of last Friday morning, 667 American soldiers have died in Afghanistan, Pakistan, and Uzbekistan in support of the war. Of those, 449 were killed by hostile fire.
The report says that a further 68 were killed outside the region in support of the war, in places from Cuba to Kenya and the Philippines to Seychelles. Four CIA officers and one military civilian have also been killed in that time.