WASHINGTON — President Bush sent American troops to Georgia on Wednesday to oversee a "vigorous and ongoing" humanitarian mission, in a direct challenge to Russia's display of military dominance over the region. His action came after Russian soldiers moved into two strategic Georgian cities in what he and Georgian officials called a violation of the cease-fire Russia signed the day before.
Bush demanded that Russia abide by the cease-fire and withdraw its forces or risk its place in "the diplomatic, political, economic and security structures of the 21st century." It was his strongest warning yet of potential retaliation against Russia over the conflict.
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.
On a day when 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," 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 Bush's statement in Washington.
Bush spoke in the Rose Garden of the White House, flanked by his secretaries of state and defense, Condoleezza Rice and Robert Gates. He said that Rice would fly to France to support its mediation efforts and then to Georgia "to continue our efforts to rally the free world in the defense of a free Georgia."
Bush's remarks, like the military operation he ordered, reflected a growing apprehension within the White House over Russia's offensive, as well as mounting frustration that Prime Minister Vladimir Putin of Russia, whom Bush often calls a friend, was unmoved by appeals for moderation. Underscoring the urgency, Bush, who had remained at the Olympics in Beijing while the conflict erupted, postponed a planned trip to his ranch in Crawford, Texas.
The first relief aircraft, a C-17 transporter carrying medical supplies and materials for shelter for thousands displaced by the fighting, arrived in Tbilisi, Georgia's capital, on Wednesday; a second was due today.
Rice called her Russian counterpart, Sergey V. Lavrov, and informed him about the relief operation. The presence of American troops to help the aid mission would also allow the United States to monitor whether Russia was honoring the cease-fire brokered by President Nicolas Sarkozy of France.
At a news conference at the State Department, Rice evoked some of the darkest memories of the Cold War, though she stopped well short of promises of direct military support to Georgia.
"This is not 1968, and the invasion of Czechoslovakia, where Russia can invade its neighbor, occupy a capital, overthrow a government and get away with it," she said. "Things have changed."
She and Bush gave credence to Georgia's accusations that Russian forces continued to operate in violation of the cease-fire. Russia insisted that all of its operations were permitted under the agreement.
The cease-fire included a provision that required Russian forces to withdraw to their "normal bases of encampment" but also allowed them to "implement additional security measures."
A senior American official said the vague language "would allow the Russians to do almost anything."
Only hours after the agreement was reached, a Russian tank battalion occupied parts of Gori, a strategic city in central Georgia. Hundreds of additional Russian soldiers also poured over the border from Russia into South Ossetia, accompanied by fuel trucks and attack helicopters.
Gori is only 40 miles from the capital, and the presence of Russian forces there frayed nerves as rumors circulated of an attack on Tbilisi itself.
Bush cited reports that Russians had taken up positions in Poti, a port city on the Black Sea, and were blowing up Georgian ships. Russian officials denied that troops had occupied any cities, but some of the statements appeared to rest on technicalities of what constituted occupation.
In Russia, Lavrov, the foreign minister, warned the Bush administration that it risked a breach with Russia by throwing its support so strongly behind Georgia and its president.
"We understand that this current Georgian leadership is a special project of the United States," he said, "but one day the United States will have to choose between defending its prestige over a virtual project or real partnership" with Russia.
Bush's remarks were the toughest yet in the conflict. "Russia's ongoing actions raise serious questions about its intentions in Georgia and the region," he said. "In recent years, Russia has sought to integrate into the diplomatic, political, economic, and security structures of the 21st century. The United States has supported those efforts. Now Russia is putting its aspirations at risk by taking actions in Georgia that are inconsistent with the principles of those institutions."