This summer, The Washington Post will start charging frequent users of its Web site. (Bill O'Leary/The Washington Post)

This summer, The Washington Post will start charging frequent users of its Web site, asking those who look at more than 20 articles or multimedia features a month to pay a fee, although the company has not decided how much it will charge.

The paper said, however, that it will exempt large parts of its audience from having to pay the fees. Its home-delivery subscribers will have free access to all of The Post’s digital products, and students, teachers, school administrators, government employees and military personnel will have unlimited access to the Web site while in their schools and workplaces.

Access to The Post’s home page, section front pages and classified ads will not be limited.

The step, while modest compared with moves by some other publications, marks a major change for The Post, which has shied away from what is known as a paywall for fear of driving away readers and online advertisers. It now joins a long list of other daily publications that charge for content, including the Wall Street Journal, the Financial Times, the Boston Globe and the New York Times.

“News consumers are savvy; they understand the high cost of a top-quality news gathering operation and the importance of maintaining the kind of in-depth reporting for which The Post is known,” Katharine Weymouth, publisher of The Post, said in a statement. “Our digital package is a valuable one, and we are going to ask our readers to pay for it and help support our news gathering as they have done for many years with the print edition.”

Moreover, she said later in a meeting for staff members, charging more and more for print subscriptions while giving away content online was “a wholly irrational proposal for our readers.”

People familiar with The Post’s online efforts say the company is planning to release a new iPad application that it believes will help attract subscribers.

Donald E. Graham, chairman and chief executive of The Washington Post Co., has been among those in the journalism industry most concerned about possible adverse effects of charging for online content, but he has agreed to the model.

“We are obviously looking at paywalls of every type. But the reason we haven’t adopted one yet is that we haven’t found one that actually adds to profits,” Graham said at the UBS Global Media and Communications Conference in December. “But we are going to continue to study every model of paywall and think about that, as well as think about keeping it free.”

Unlike the New York Times and the Wall Street Journal, The Post has traditionally been a local business, pulling in large amounts of advertising from area merchants eager to reach the print edition’s audience. By contrast, 90 percent of The Post’s online audience is outside the Washington area.

Graham said at the New York conference that a paywall could drive away some of the paper’s digital audience and thus push away advertisers and cost the paper “a very significant amount of digital advertising.” Digital advertising makes up about a fifth of total advertising for the newspaper, Post executives said at the staff meeting Monday.

But Monday, Weymouth said in an interview that “we really are a 24-7 publisher of news. To separate our print from our online subscription models doesn’t make sense anymore. We’ve watched our peers in the industry, and we think the metered model is the best way to keep our reach while asking our readers to help pay for the quality journalism we are known for.”

Revenue generated from the company’s online publishing activities, primarily the Post Web site and Slate, increased 5 percent to $110.6 million in 2012, up from $105.8 million in 2011. Most of that was online display advertising, from which revenue increased 6 percent in 2012. Online classified-ad revenue decreased 1 percent in 2012.

Weymouth said The Post is still studying what fee will work best.

The Washington Business Journal reported last month that The Post had been surveying users about potential options. It quoted one user as saying that The Post had inquired about seven-day delivery and unlimited Web access for $24.95 a month, unlimited Web access without a print subscription for $14.95 a month, and Sunday delivery and unlimited Web access for $7.95 a month.

“We’re definitely engaging in research to come to the right price,” Weymouth said, but she said those figures might not be where The Post ends up.

In response to a question at the staff meeting, Washington Post Executive Editor Marty Baron said that there were about 20 open positions in the newsroom at the beginning of the year and that the staff would be reduced by “another 10 to 15 by the end of the year.” He said that figure did not include new hires for video content on the Web. Counting those, he said, the size of the newsroom “won’t be that much different.”