"Our enemy is trying to weaken us and we must respond by consolidating our main values - liberty and democracy."
However, diplomats and analysts have warned that the vote will have to be conducted fairly if Georgia is to obtain Western support in a row over Abkhazia and South Ossetia - two separatist regions backed by Russia.
Georgia's image as a "rare beacon of democracy" in the former Soviet Union was tarred in November when Saakashvili sent in riot troops to crush protests.
Opponents said he rigged a January presidential poll, a charge he denies.
The opposition also say the authorities are planning to rig the poll again and have threatened mass demonstrations if this happens.
Levan Gachechiladze, leader of the opposition coalition, said: "The election campaign has shown that authorities plan to falsify this election again."
Gachechiladze also said he would call on supporters to force their way into the electoral commission office if authorities "do not release the real results of the vote".
"The people have every right to protect their votes," he said.
The Organisation for Security and Cooperation in Europe (OSCE),the main Western election monitoring body, has sent 550 observers to monitor the vote and is to deliver a verdict on its conduct on Thursday.
Saakashvili became the so-called "darling of the West" after he gained power in 2003, promising market reforms, a greater adherence to democracy and re-orienting the country towards the European mainstream.
But the opposition says that Saakashvili's rhetoric about democracy masks his intolerance of dissent.
Nato, too, which has offered Tbilisi a path to eventual membership, has said it will be watching to ensure the election will be fair.