WASHINGTON — Hillary Clinton said on Sunday that the Islamic State had become “the most effective recruiter in the world” and that the only solution was to engage American technology companies in blocking or taking down militant websites, videos and encrypted communications.

“You are going to hear all the familiar complaints: ‘freedom of speech,’ ” Mrs. Clinton said in an hourlong speech and question-and-answer session at the Saban Forum, an annual gathering at the Brookings Institution that focuses mostly on Israel’s security issues.

In a reference to Silicon Valley’s reverence for disruptive technologies, Mrs. Clinton said, “We need to put the great disrupters at work at disrupting ISIS,” an acronym used for the militant group.

It was the second time in two weeks that Mrs. Clinton, the front-runner for the Democratic presidential nomination, had thrown herself into the brewing battle between Silicon Valley and the government over what steps should be taken to block the use of Facebook, YouTube, Snapchat and a range of encrypted apps that are adopted by terrorist groups.