The decision to send the American military, even on a humanitarian mission, deepened the United States’ commitment to Georgia and America’s allies in the former Soviet sphere, just as Russia has been determined to reassert its control in the area.

Image Women from a Georgian village stood by the road to Tbilisi, Georgias capital, after fleeing their homes on Wednesday afternoon when armed Ossetians arrived. Credit... Justyna Mielnikiewicz for The New York Times

On a day the White House evoked emotional memories of the cold war, a senior Pentagon official said the relief effort was intended “to show to Russia that we can come to the aid of a European ally, and that we can do it at will, whenever and wherever we want.” At a minimum, American forces in Georgia will test Russia’s pledge to allow relief supplies into the country; they could also deter further Russian attacks, though at the risk of a potential military confrontation.

“We expect Russia to ensure that all lines of communication and transport, including seaports, airports, roads and airspace, remain open for the delivery of humanitarian assistance and for civilian transit,” Mr. Bush said. “We expect Russia to meet its commitment to cease all military activities in Georgia, and we expect all Russian forces that entered Georgia in recent days to withdraw from that country.”

In Georgia, President Mikheil Saakashvili, who has sharply criticized what he called a failure of the West to support his country, declared the relief operation a “turning point” in the conflict, which began on Thursday when Georgian forces tried to establish control in the breakaway region of South Ossetia, only to be routed by the Russians.

“We were unhappy with the initial actions of the American officials, because they were perceived by the Russians as green lines, basically, but this one was very strong,” he said in a telephone interview after Mr. Bush’s statement in Washington.