Britain's Liberal Party voted overwhelmingly in favor of a merger with the Social Democrats in a bid to consolidate the nation's disjointed center into a force that could shake the Conservative hold on government. Party delegates passed the merger amendment by a vote of 2,099 to 385 at a special convention in the west coast resort city of Blackpool. The Social Democrats hold a similar meeting this week. If accepted there, the merger question will be put to a vote of the entire membership of both parties. The center parties, paired in the past in a loose alliance, are taking the first steps toward a merger since their defeat last June, when Prime Minister Margaret Thatcher's Conservatives won a third term.