Rupert Murdoch played offense on Thursday, embarking on a rare publicity campaign to extol the economic prospects of News Corporation’s newspapers after announcing earlier that they would be spun off into a separate company.


In a phone interview, Mr. Murdoch said he would not allow the publishing company — which will include The Wall Street Journal, The New York Post, The Times of London and the HarperCollins book division, among other assets — to struggle financially without the safety net of News Corporation’s fast-growing and lucrative cable channels.


“Dow Jones is a very viable company and The Wall Street Journal is a very viable newspaper,” said Mr. Murdoch, News Corporation’s chairman and chief executive. As for newsroom employees who have expressed anxiety about not having entertainment assets like Fox News and 20th Century Fox to prop up the newspaper business, Mr. Murdoch said they “shouldn’t feel like they’ve got a crutch.”


Chase Carey, News Corporation’s chief operating officer, who was also on the interview, added that putting the newspapers in a separate company would give them “the impetus to grow and fulfill their potential.”


Their comments represented a vigorous endorsement of a struggling industry, and a rebuttal to critics who portrayed the newspaper division as an aging business with little prospect for growth. In a memo to his staff announcing the move, Mr. Murdoch seemed to relish the chance to prove people wrong about his newspapers when he wrote, “our publishing businesses are greatly undervalued by the skeptics.”


Still, the decision marked a rare change of heart for Mr. Murdoch, who built his company on newspapers and has for years rejected proposals to spin them off. But as the financial challenges facing print journalism worsened, and a phone-hacking scandal in Britain brought reputational damage to News Corporation, calls from shareholders to sever the papers grew louder.


Those sentiments were also being expressed by Mr. Murdoch’s top lieutenants, Mr. Carey and David DeVoe, the chief financial officer. Eventually, Mr. Murdoch was convinced that separating the publishing and entertainment units was the right thing to do, and the move was approved by the company’s board Wednesday evening.


“I don’t want to hide the fact that I put my life into this,” Mr. Murdoch said Thursday in a conference call with analysts. “It’s a very big move and a very big decision for me to move forward with this.”


 Analysts estimate that the new publishing company in its entirety — including nearly 175 newspapers — will be worth less than the $5 billion Mr. Murdoch paid in 2007 to buy Dow Jones, publisher of The Journal, Barron’s and the Dow Jones Newswires. News Corporation shares have jumped nearly 10 percent since the company said Tuesday it was exploring a separation.


“The market has shown with other companies that it will put a higher multiple on the media and entertainment company than it will on the other,” Mr. Murdoch said in the interview.


 But he also pointed to the Viacom breakup in late 2005, in which some of that media empire’s television properties were bundled into a new company, CBS Corporation. Since the split, CBS has outpaced its former corporate sibling, with its stock rising 23.4 percent and Viacom’s gaining only 16.8 percent. “CBS was considered the orphan then, and look at what happened,” Mr. Murdoch said.


 The new company is expected to have a strong balance sheet, with one person adding that it will have more cash than debt. In addition to newspapers and HarperCollins, it will include an education division and other assets based in Australia.


 Mr. Murdoch said the timing of the spinoff was unrelated to the phone-hacking scandal in Britain, which has embarrassed the company and forced it to drop its bid for the 60 percent of British Sky Broadcasting it did not already own. “We reached a consensus and a feeling that it was right and there was no point” leaving the company as one combined business, he said.


 Asked by Fox Business Network whether News Corporation still wanted to own BSkyB, he said: “We’ve moved on from our thinking in that. That was billions and billions of dollars and if Britain doesn’t want them, we’ll find a place to put them here.”