But by refusing to release the emails, Mr. Obama is following a well-worn precedent that he and his predecessors have established. Mr. Obama has repeatedly resisted efforts by Congress to turn over the president’s private communications, which by law are exempt from Freedom of Information laws that are often used to pry information out of other parts of an administration.

Former presidents of both parties have done the same, often insisting that to do otherwise would open the president’s most sensitive deliberations to congressional and public inspection.

“Direct communications by the president and his senior advisers are really at the very center of what is trying to be protected by executive privilege and the separation of powers,” said William Burck, a deputy counsel for President George W. Bush. He called the decision by Mr. Obama’s administration “very reasonable” and praised the president for following Mr. Bush’s practice.

The emails released on Friday show Mrs. Clinton received at least some indication that J. Christopher Stevens, the United States ambassador to Libya, was concerned about security in Benghazi more than a year before he was killed in the attack there.

An email sent to Mrs. Clinton in April 2011 said Mr. Stevens would meet with Libyan officials to “make a written request for better security at the hotel and for better security-related coordination.” How much Mrs. Clinton knew about the deteriorating situation in Benghazi was a focus of Republican questions at a congressional hearing this month.

One email a few days after the Benghazi attack shows Jake Sullivan, a top aide, telling Mrs. Clinton that Susan E. Rice, the United Nations ambassador, went on the Sunday talk shows and “did make clear our view that this started spontaneously and then evolved.” But a week later, after Ms. Rice spoke about a video prompting the attack, Mr. Sullivan wrote Mrs. Clinton that “you never said spontaneous or characterized the motives.”

The emails also highlighted how much advice Mrs. Clinton received from Sidney Blumenthal, a family friend who had been barred by the White House from working at the State Department. In one, Mr. Blumenthal suggests that Seymour Hersh, an investigative journalist, had discovered that Col. Muammar el-Qaddafi, the leader of Libya, was in Chad.