As many as 100,000 people are expected to demonstrate Thursday against the president.
The war broadened Monday as Russian troops moved beyond rebel provinces into Georgia proper.
Georgian President Saakashvili called for international mediation over the breakaway region in a conflict some see as East vs. West.
The Columbia-educated president's party is expected to retain power in Wednesday's parliamentary elections. In an interview, he describes why he sees the country as the front line against Russian aggression.
The pro-West president called Saturday's snap polls after being criticized for authoritarianism. With early results giving him 48 percent of the vote, opponents protest fraud.