In Argentina, groups of youths stoned store and bank windows, lit fires and fought with police in downtown Buenos Aires yesterday at the end of an otherwise peaceful march by left-leaning parties protesting President Clinton’s visit. About 50 youths, their faces covered with bandanas, threw rocks and Molotov cocktails at the windows of several banks and shops. Neighbors extinguished the fires with buckets of water. Police dispersed the youth with tear gas after they broke windows. No arrests were immediately reported. The march was organized by parties along the avenue in the northern section of the capital, where Argentine President Carlos Menem was scheduled to host a state dinner for Clinton. Marchers, many with Che Guevara T-shirts and carrying red flags, chanted, “Clinton, get out of Argentina!” And they burned American flags.