They flee by the thousands -- in horse-drawn carts stacked high with clothes and furniture; on bicycles balancing precarious bundles; on foot, arms laden with any belongings they can carry. Since Abkhazian rebels broke a Russian- mediated cease-fire and drove Georgian forces out of the Black Sea region, seizing its capital, Sukhumi, an estimated 200,000 Georgians are thought to have been uprooted. Some have been trudging for days through the bitter-cold, snow-covered mountains of the Caucasus, headed mainly into cities of western Georgia. In Sukhumi the Abkhazian insurgents are accused of having carried out mass ''ethnic cleansing,'' looting and plundering the former homes of Georgians, Russians and people of other nationalities. In a belated move to support Georgia, which reluctantly joined the Russia- dominated Commonwealth of Independent States only two weeks ago, Moscow has cut off energy and fuel supplies to Abkhazia and has sealed the border with the rebel-held region. Still, Georgian officials fear that their country faces complete collapse unless the Kremlin sends Russian troops to help recapture the Black Sea region and quash the spreading rebellion in the Transcaucasian state.