As Washington tries to rebuild its strained relationships in Latin America, China is stepping in vigorously, offering countries across the region large amounts of money while they struggle with sharply slowing economies, a plunge in commodity prices and restricted access to credit. In recent weeks, China has been negotiating deals to double a development fund in Venezuela to $12 billion, lend Ecuador at least $1 billion to build a hydroelectric plant, provide Argentina with access to more than $10 billion in Chinese currency and lend Brazil