The New York Times Co. said Thursday that chief executive Janet Robinson, who helped the paper broaden its reach nationally and make more money online, will step down at the end of the year. She will be replaced on an interim basis by Arthur Sulzberger Jr., publisher of the flagship paper and chairman of the company.

Robinson, 61, became CEO at the end of 2004, and presided over difficult times at the paper. During her tenure, the paper slashed staff as print advertising revenue declined. The company sold most of its midtown Manhattan headquarters in 2009 to raise cash and then leased a portion of it back. The Times also borrowed money that year from Mexican billionaire Carlos Slim at steep interest rates before refinancing this year and paying it back early.

Robinson said in a statement that she leaves the company with "mixed emotions" after working at the paper for 28 years. She also expressed pride for helping the paper navigate the transition from traditional print journalism to the digital world.

In March, the company began charging users for full online access to the paper's content. By the end of September, it had 324,000 paying digital subscribers, bringing Times' combined paper and online subscribers to 1.2 million. Digital advertising now makes up 14 percent of total revenue, up from 8 percent in 2006.

"Obviously, the last few years have been tough as, together, we have navigated one of the most difficult periods in publishing history," she said in a memo to staff on Thursday. She said the company is on firmer financial footing and has a digital strategy in place "that should serve the company well for many years into the future."

Robinson will serve as a consultant for one year during which she will be paid $4.5 million, according to a securities filing.

Sulzberger credited Robinson with pushing the New York Times to become a truly national newspaper starting in the late 1990s. Today, more than half of the paper's subscribers live outside of New York.

"It took huge courage and vision on Janet's part to create and to successfully implement our national edition. We will always be in her debt," he said in a staff memo.

The company is initiating a search for a new chief executive.

Newspaper analyst Ken Doctor said the Times' digital operation is the most successful in the newspaper industry, but it hasn't been enough to overcome the erosion of print advertising.

When Robinson took over as CEO, the Times Co. earned $293 million on revenue of $3.3 billion. This year, analysts project earnings of $93 million on revenue of $2.3 billion.

There is little reason to expect that the situation will improve next year, which is one reason Doctor believes newspaper industry executives such as Robinson are calling it quits. The Times Co.'s top digital executive, Martin Nisenholtz, also recently announced his plans to retire at the end of the year. Earlier this week, Los Angeles Times editor Russ Stanton stepped down after several years of staff layoffs.

"The headaches aren't over because print advertising is in a death spiral," Doctor said. "The New York Times is ahead of the curve digitally, but there are still some blind turns ahead. Their future is still not secure."