WASHINGTON — For months, Facebook, Twitter and Google have grappled with criticism over the misuse of their services by foreign operatives and the disproportionate influence their platforms have over people’s thinking.

On Wednesday, when Sheryl Sandberg, Facebook’s chief operating officer, and Jack Dorsey, Twitter’s chief executive, will appear in Washington to testify on those issues, they plan to answer lawmakers’ questions using two main tactics: a conciliatory and apologetic approach, as well as a rundown of the growing number of efforts that the companies have taken to deal with manipulation and disinformation problems.

“We were too slow to spot this and too slow to act. That’s on us,” Ms. Sandberg said in prepared testimony that was reviewed by The New York Times. “We’re getting better at finding and combating our adversaries, from financially motivated troll farms to sophisticated military intelligence operations.”

In testimony that was posted online on Tuesday, Mr. Dorsey said, “Twitter is approaching these challenges with a simple question: How do we earn more trust from the people using our service? We know the way to earn more trust around how we make decisions on our platform is to be as transparent as possible.”