The companies showed fissures in their view on regulations. Facebook has vocally supported internet regulations in a major advertising blitz on television and in newspapers. In the hearing, Mr. Zuckerberg suggested specific regulatory reforms to a key legal shield, known as Section 230 of the Communications Decency Act, that has helped Facebook and other Silicon Valley internet giants thrive.

The legal shield protects companies that host and moderate third-party content, and says companies like Google and Twitter are simply intermediaries of their user-generated content. Democrats have argued that with that protection, companies aren’t motivated to remove disinformation. Republicans accuse the companies of using the shield to moderate too much and to take down content that doesn’t represent their political viewpoints.

“I believe that Section 230 would benefit from thoughtful changes to make it work better for people,” Mr. Zuckerberg said in the statement.

He proposed that liability protection for companies be conditional on their ability to fight the spread of certain types of unlawful content. He said platforms should be required to demonstrate that they have systems in place for identifying unlawful content and removing it. Reforms, he said, should be different for smaller social networks, which wouldn’t have the same resources like Facebook to meet new requirements.

Mr. Pichai and Mr. Dorsey said they supported requirements of transparency in content moderation but fell short of agreeing with Mr. Zuckerberg’s other ideas. Mr. Dorsey said that it would be very difficult to distinguish a large platform from a smaller one.

Lawmakers did not appear to be won over.

“There’s a lot of smugness among you,” said Representative Bill Johnson, a Republican of Ohio. “There’s this air of untouchable-ness in your responses to many of the tough questions that you’re being asked.”

Kate Conger and Daisuke Wakabayashi contributed reporting.

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