MENLO PARK, Calif. » Facebook’s long-rumored plan to directly host articles from news organizations will start on Wednesday, concluding months of delicate negotiations between the Internet giant and publishers that covet its huge audience but fear its growing power.

Nine media companies, including NBC News and The New York Times, have agreed to the deal, despite concerns that their participation could eventually undermine their own businesses.

The program will begin with a few articles but is expected to expand quickly. Users of iPhones will see glossy cover videos and photos tagged with map coordinates. Most important for impatient smartphone users, the company says, the so-called instant articles will load up to 10 times faster than they normally would since readers stay on Facebook rather than follow a link to another site.

Facebook has gone to unusual lengths to court the publishers participating in the project, some details of which were previously published by The New York Times and The Wall Street Journal.

The news publishers can either sell and embed advertisements in the articles, keeping all of the revenue, or allow Facebook to sell ads, with the social network getting 30 percent of the proceeds. Facebook is also permitting the news companies to collect data about the people reading the articles with the same tools they use to track visitors to their own sites.

For publishers, the Facebook initiative represents the latest in a series of existential balancing acts. The social network, which has more than 1.4 billion active users worldwide, captures more attention of mobile users — and prompts more visits to news sites — than virtually any other service.

Publishers have little choice but to cooperate with Facebook, said Vivian Schiller, a former executive at NBC, The New York Times and Twitter who now advises media companies and brands. “That’s where the audience is,” Ms. Schiller said. “It’s too massive to ignore.”

But Facebook’s role as a powerful distributor of news makes many people in the industry uneasy. The fear is that it could become more of a destination than their own sites for the work they produce, drawing away readers and advertising.

James Bennet, editor in chief of The Atlantic, one of the project’s initial publications, said that publishing pieces through instant articles means “losing control over the means of your distribution.” On the other hand, he said, “we’re trying to get out stories to as many people as possible, and at the same time, continue to build a core, loyal, enthusiastic audience.”

Facebook has a long history of changing the algorithm that determines what people see in their feeds. Zynga, the mobile gaming company, built its business on Facebook only to lose much of its traffic when the company changed the rules to make a user’s game activity less visible to friends.

Last year, Facebook decided to downgrade the prominence of viral content like cat videos and promote “high quality” news content. A month ago, it changed course again to highlight personal posts by users’ friends and family.

Chris Cox, Facebook’s chief product officer, was unapologetic about the shifting rules. In an interview at the company’s Silicon Valley headquarters, he said that Facebook’s mission was to give its users what they wanted most.

“We see ourselves as first helping people connect with friends and family,” Mr. Cox said. “And second, helping people be informed about the world around them.”

The Atlantic is going into the Facebook deal with its eyes open, Mr. Bennet said, referring to the prospect that Facebook might be in a position to dictate less favorable terms if its importance to publishers increases.

Five American organizations are initially participating in the instant articles project and will publish one item each on Wednesday in the new format: BuzzFeed, National Geographic, The Atlantic, NBC News and The Times.

Four European outlets are also joining: The Guardian, BBC News, Bild and Spiegel Online. Over time, Facebook expects to add other publishers to the project, which is officially a test, and expand it beyond the iPhone version.

For The Times, Facebook represents from 14 to 16 percent of its web traffic — a figure that has doubled in recent months, according to Mark Thompson, chief executive of The New York Times Company.

“This is a chance to expand and explore whether Facebook can become an even bigger part,” Mr. Thompson said. On balance, the company felt that it was an experiment worth taking part in, he added. Articles on Facebook will not initially count against the 10 free items people who are not Times subscribers are allowed to read each month.

Facebook is offering publishers new tools to showcase their work, including interactive maps and the ability to post high-resolution photos that readers can zoom into and view from any angle.

“We’re not trying to position Facebook as a replacement for a newspaper, or a radio show that you love, or TV, at all,” Mr. Cox said. “We can be complementary.”

Facebook clearly plays an important role as a gatekeeper to news. Nearly half of American Internet users said they got news about politics and government on Facebook during the course of a week, almost as many as got such news from local television, according to a survey last year by the Pew Research Center.

Jonah Peretti, chief executive of BuzzFeed, said the instant articles format enhances the current approach of simply posting links.

“The look and feel of this feels more like an app,” Mr. Peretti said in an interview. “I think that our bundle of content will get even more compelling when it loads faster.”

Declan Moore, chief media officer of the National Geographic Society, said the appeal of instant articles was the speed with which items, even those with complex video and interactive maps, loaded once a mobile Facebook user clicked on them. “The No. 1 thing on mobile is it has to be fast,” he said.

National Geographic, which gets about 25 percent of its traffic from Facebook, is one of the most popular news outlets on the service, with 35 million fans. Mr. Moore said that National Geographic had a long history of putting its content on as many platforms as possible.

It intends to use Facebook as a way to encourage more people to sign up for membership, he said. Indeed, its first instant article, about bees, will include two ads encouraging people to join.

The New York Times has been cautious about the Facebook program, viewing it as an experiment that could help it learn more about subscribers and potential subscribers who are reading its articles on Facebook.

Unlike many news publishers, The Times generates significant revenue from digital subscriptions as well as online advertising, and the company is keenly interested in finding new ways to convert casual visitors to paid subscribers.

The publishers said they did not plan to put more than a few articles a week into the new format, at least at first.

Facebook says it wants to be a good partner to news organizations. It began discussing its idea with around 20 publishers last August and tried to address the concerns they raised.

“We’re starting with something that we think is going to work for some publishers for some articles and for some business models,” Mr. Cox said. “We’re not trying to go, like, suck in and devour everything.”

Vindu Goel reported from Menlo Park, Calif., and Ravi Somaiya from New York.

© 2015 The New York Times Company