NEW YORK — Apple Inc. announced a subscription system Tuesday for buying newspapers and magazines on iPhone and iPad applications, making it easier for publishers to mine the popular mobile devices for more revenue.

The update enables publishers to sell subscriptions by the week, month, year or other period of time, instead of asking readers to buy each issue separately. The added convenience promises to help publishers sell more digital copies as they look to smart phones and tablet computers to replace some of the revenue that has disappeared over the past few years as readers and advertisers migrated from print editions.

But publishers won’t be allowed to automatically collect personal information about people who buy subscriptions through the apps. That data is prized by publishers because they use it for marketing purposes.

Instead, subscribers who sign up through an app on an Apple device will be given the option to share their information with publishers, a choice that most people decline.

Apple will take its standard 30 percent cut from all app and content sales made in its iTunes store, which peddles a variety of music, movies, games and e-books. This new subscription system also applies to video and music services – for instance, the app for Netflix.

Content providers that don’t want to automatically give Apple a slice of the revenue can try to sell subscriptions outside the app, too. One way to do that would be through the Web browser, although that might prove too much of a hassle for people already used to buying apps, music and other things on iTunes.