Ms. Sandberg is a veteran of Washington politics. She was the chief of staff to the former Treasury Secretary Lawrence Summers during the Clinton administration, and now oversees policy for Facebook, among other things.
Mr. Dorsey, known for his taciturn style, has been on a media blitz in recent weeks as Twitter has tried to shore up its reputation. He is not well known in Washington and will have to defend Twitter from accusations of political bias in a manner that doesn’t further rile lawmakers.
Both executives have been preparing for the hearings for several weeks. They each have been coached by company lawyers and Facebook and Twitter’s Washington policy staffs on what questions specific lawmakers may ask and which ones may use the hearings to level new accusations or threats of regulations, according to people involved in the preparations, who were not authorized to talk publicly. Ms. Sandberg and Mr. Dorsey have been advised to appear contrite, to be direct with their responses and to be patient if interrupted, the people said.
Ms. Sandberg and Mr. Dorsey met with several lawmakers on Tuesday, ahead of the hearings. Both met with members of the Senate Intelligence Committee, including Mr. Burr, as well as Mark Warner, Democrat of Virginia, and Ron Wyden, Democrat of Oregon, according to committee aides.
The Senate hearing wasn’t expected to yield many new revelations on foreign interference, and some lawmakers were expected to veer into other topics. Marco Rubio, Republican of Florida, and Tom Cotton, Republican of Arkansas, would most likely raise concerns of content biases by social media sites that stifle conservative views, according to committee aides. And Mr. Wyden was expected to focus on online privacy and the potential need for regulations.
In particular, lawmakers may press the executives on how vulnerable their sites are ahead of the midterms.
Senior Trump administration intelligence officials have warned of the threat of foreign interference. Facebook, Twitter, and Google have recently identified foreign influence campaigns linked to Iran and Russia, though they also said they could not conclusively determine that those were meant to interfere in the midterms.