LILLE, France, March 123 2008 - Hundreds of trucks trying to get toBritain were blocked Wednesday at ports in northern France because of strikeaction by cross-Channel ferry workers, officials said.   Between 700 and 800 trucks were waiting up to 10 hours to board ferries atthe port of Dunkirk, while lines of trucks stretched up to six kilometres(four miles) at Calais, traffic officials said.   The queues were caused by a walkout that began on February 27 by officerson five Seafrance ferries that travel between Calais and Dover in England.They are demanding better pay and conditions.   Truckers have been using other companies' ferries as well as the ChannelTunnel, but the Seafrance strike has severely disrupted cross-Channel traffic.   A British local council on the other side of the Channel, where truckersare also backed up along approach roads to the ports, says the Frenchgovernment should pay for the chaos caused by the striking ferry workers.   A spokesman for Kent County Council in southeast England said the authorityhad written to French President Nicolas Sarkozy to ask for compensation.