After the most crucial election battle of his life, Gerry Adams, the political leader of the Sinn Féin, is widely expected to win a Northern Ireland seat in the British parliamentary election today. There are no independent polls, but virtually all experts, including diplomats and British and Irish Republic officials, say Adams will win the seat in predominantly Roman Catholic West Belfast that he lost five years ago to Dr. Joe Hedron, a mainstream Catholic nationalist who is running for re-election.