The "domino theory" so popular among many Reagan administration officials and other North Americans finds no echo here. The theory holds that if the leftwing insurrection that triumphed in Nicaraua sweeps through the rest of Central America. It will eventually bring down Mexico. and even Imperil the United States. For instance. most Mexicans do not think a guerrilla takeover in Guatemala would be the main factor in determining their countrys future. At most. Mexicans see the key factor in such a hypothetical takeover as creating a refugee problem and causing political ripples in the poor southern border province of Chiapas. In short. US and Mexican analysts say that upheavals to the south would affect the whole country.