Barack Obama took part in a prayer service - a tradition that dates to the inauguration of George Washington, the first US president. Obama and the first lady, Michelle Obama, were in the front pew at the National Cathedral as the service began Wednesday. Joining them there were Vice President Joe Biden and his wife, Jill. Former President Bill Clinton and his wife, Secretary of State nominee Hillary Clinton, were also in the front row with the first family. The service will include a prayer for the US, scripture readings and hymns delivered by religious leaders of a variety of faiths. The new president was not scheduled to make remarks.