WASHINGTON — President Obama offered a robust defense of newly revealed surveillance programs on Friday as more classified secrets spilled into public, complicating a summit meeting with China’s new president focused partly on human rights and cybersecurity.

Mr. Obama departed from his script at a health care event in California to try to reassure Americans that he had not abused government authority by collecting telephone call logs and foreigners’ e-mail messages. But the disclosure hours later of secret contingency planning to target other countries for possible cyberattacks made his get-together with President Xi Jinping later in the day all the more awkward because cyberattacks by the Chinese are high on the American agenda.

The latest of three documents published over three days by the British newspaper The Guardian added to the understanding of the Obama administration’s approach to national security in an age of multifaceted threats and became another factor in the renewed debate over the balance between privacy and security.

The identity of the person who gave those documents to The Guardian and The Washington Post is not known, but The Post has described its source as a career intelligence officer angry at “what he believes to be a gross intrusion on privacy” by the Obama administration.