WASHINGTON — President-elect Joe Biden is building out his administration with several key picks for national security and foreign policy roles. John Kerry, a former secretary of state, will lead the incoming administration’s effort to combat climate change. Alejandro Mayorkas will be nominated as the secretary for the Department of Homeland Security. Biden also plans to nominate Antony Blinken as his secretary of state, according to multiple people familiar with the Biden team’s planning. Blinken, 58, served as deputy secretary of state and deputy national security adviser during the Obama administration and has close ties with Biden.