With weeks-old snow still lining some Boston streets, the city has pushed back the start of its extended street sweeping program. The initiative was to run from the beginning of March through the end of December in the North End, South End, and starting this year, Beacon Hill. The city, however, announced via Twitter that the sweeping would be delayed in those neighborhoods. “Due to roadway conditions, posted street sweeping for the South End, North End, and Beacon Hill is canceled for the entire week of March 4,” the city tweeted. The Department of Public Works will reevaluate conditions to begin sweeping on the week of March 11, the city said.