“Whether it or not it was intended to help one candidate or another, I don’t know,” said Mr. Gates, who also served as C.I.A. director under President Bush. “But I think it clearly was aimed at discrediting our elections, and I think it was aimed certainly at weakening Mrs. Clinton.

Speaking on NBC’s “Meet the Press,” he stopped short of saying the meddling was intended to help Mr. Trump, and said the best course of action to respond to the cyberattacks was unclear.

Asked why Mr. Trump appeared not to be taking the allegations against Russia seriously, Mr. Gates speculated that the president-elect “felt the way this information came out through newspaper stories and so on was somehow intended to delegitimize his victory in the election and that he’s reacting to that rather than ‘the facts on the ground,’ as it were.”

Mr. Trump has chosen to receive intelligence briefs only occasionally.

Podesta said the F.B.I. contacted him only once.

Few people were as directly affected by the hacking as John D. Podesta, the chairman of Mrs. Clinton’s campaign. But on Sunday he suggested that there was hardly a zealous effort by the F.B.I. to investigate, adding that the only time he had been contacted by federal agents was two days after his hacked personal emails began appearing on WikiLeaks.

Mr. Podesta said he had believed that some of the documents related to the Democratic National Committee published by WikiLeaks last summer could have come from his account. But he only became certain that his account had been fully compromised when WikiLeaks began publishing its contents on Oct. 7.

“Two days later, the F.B.I. contacted me, and the first thing the agent said to me was, ‘I don’t know if you’re aware, but your email account might have been hacked,’” Mr. Podesta said.