The European Union  and Germany, in particular, with its strong ties to Russia  called on both sides to stand down and scheduled meetings to press their concerns. At the United Nations, members of the Security Council met informally to discuss a possible response, but one Security Council diplomat said it remained uncertain whether much could be done.

“Strategically, the Russians have been sending signals that they really wanted to flex their muscles, and they’re upset about Kosovo,” the diplomat said. He was alluding to Russia’s anger at the West for recognizing Kosovo’s independence from Serbia.

Indeed, the decision by the United States and Europe to recognize Kosovo may well have paved the way for Russia’s lightning-fast decision to send troops to back the separatists in South Ossetia. During one meeting on Kosovo in Brussels this year, Mr. Lavrov, the foreign minister, warned Ms. Rice and European diplomats that if they recognized Kosovo, they would be setting a precedent for South Ossetia and other breakaway provinces.

For the Bush administration, the choice now becomes whether backing Georgia  which, more than any other former Soviet republic has allied with the United States  on the South Ossetia issue is worth alienating Russia at a time when getting Russia’s help to rein in Iran’s nuclear ambitions is at the top of the United States’ foreign policy agenda.

One United Nations diplomat joked on Saturday that “if someone went to the Russians and said, ‘OK, Kosovo for Iran,’ we’d have a deal.”

That might be hyperbole, but there is a growing feeling among some officials in the Bush administration that perhaps the United States cannot have it all, and may have to choose its priorities, particularly when it comes to Russia.

The Bush administration’s strong support for Georgia  including the training of Georgia’s military and arms support  came, in part, as a reward for its support of the United States in Iraq. The United States has held Georgia up as a beacon of democracy in the former Soviet Union; it was supposed to be an example to other former Soviet republics of the benefits of tilting to the West.