UPDATE 2-US says warned Georgia against Russia fight

(Recasts; adds details, comments throughout)

By Susan Cornwell

WASHINGTON, Aug 19 (Reuters) - The United States warned Georgia against a fight with Russia, a senior U.S. diplomat said on Tuesday as Washington demanded Moscow withdraw its forces more quickly from the former Soviet republic.

"Our message was consistent to our Georgian colleagues ... 'Avoid a direct military confrontation with Russia at all costs. You cannot prevail. It simply is not possible,'" said Matt Bryza, the State Department diplomat who was sent to Georgia after the crisis erupted.

In some of the most explicit criticism from Washington of Georgia's actions, Bryza said the United States told Tbilisi that the Georgian military would be no match for Russia.

"Russia is 30 times as big as Georgia, its military is several times as large," he told reporters.

"It can almost instantaneously roll tanks in. And then even if you succeed miraculously in stopping the tanks, and the infantry, and the mechanized infantry, which move very quickly, it's the air power that's finally going to get you. And that is what happened."

Conflict between Georgia and Russia erupted when Georgia tried to reimpose control over the breakaway, pro-Russian South Ossetia region on Aug. 7-8. Russia responded with a massive counter-attack that overwhelmed Georgian forces.

Russia then moved troops beyond South Ossetia and a second separatist region, Abkhazia, and into Georgian territory.