By Steve Holland WASHINGTON (Reuters) -U.S. President Joe Biden and Chinese leader Xi Jinping are expected to hold a virtual summit on Monday, sources said, amid tensions over trade, human rights and military activities. Washington and Beijing have been sparring on issues from the origins of the COVID-19 pandemic to China’s expanding nuclear arsenal. U.S. officials believe direct engagement with Xi is the best way to prevent the relationship between the world’s two biggest economies from spiraling toward conflict. Beijing is also keen to avoid confrontation and focus on “positive competition,”…