Facebook’s decision to clarify its ad policy language is notable because Mark Zuckerberg, the social network’s chief executive, has repeatedly fobbed off criticism that the company had an effect on how people voted. In a post on his Facebook page over the weekend, he said that 99 percent of what people see on the site is authentic, and only a tiny amount is fake news and hoaxes.

“Over all, this makes it extremely unlikely hoaxes changed the outcome of this election in one direction or the other,” Mr. Zuckerberg wrote.

Yet within Facebook, employees and executives have been increasingly questioning their responsibilities and role in influencing the electorate, The New York Times reported on Saturday.

Facebook’s ad policy update will not stem the flow of fake news stories that spread through the news feeds that people see when they visit the social network.

Facebook has long spoken of how it helped influence and stoke democratic movements in places like the Middle East, and it tells its advertisers that it can help sway its users with ads. Facebook reaches 1.8 billion people around the globe, and the company is one of the largest distributors of news online. A Pew Research Center study said that nearly half of American adults rely on Facebook as a news source.

Google’s decision on Monday relates to the Google AdSense system that independent web publishers use to display advertising on their sites, generating revenue when ads are seen or clicked on. The advertisers pay Google, and Google pays a portion of those proceeds to the publishers. More than two million publishers use Google’s advertising network.

For some time, Google has had policies in place prohibiting misleading advertisements from its system, including promotions for counterfeit goods and weight-loss scams. Google’s new policy, which it said would go into effect “imminently,” will extend its ban on misrepresentative content to the websites its advertisements run on.