Work began yesterday on a multibillion-dollar pipeline that will carry oil from Chad through Cameroon to Africa’s Atlantic coast, a project bitterly opposed by environmentalists and human rights advocates. The World Bank is supplying 3 percent of the financing for the $3.5 billion, 670-mile pipeline project, which is being spearheaded by ExxonMobil. Opponents argue that the project will harm Cameroon’s rainforest, as well as the indigenous people and rare species that live there, and that the profits are likely to be misused by corrupt government officials rather than spent to help Chad’s desperately poor people. Recent protests against the World Bank have cited the Chad-Cameroon pipeline as a prime example of the environmentally destructive projects the body too often funds.