Ezra Klein, an analyst, columnist and television commentator who runs The Washington Post's Wonkblog, is making plans to leave the newspaper after failing to win support for a new website he wanted to create within the company, according to four people with knowledge of the negotiations.

Mr. Klein, who quickly ascended into the ranks of the Washington media establishment with a multiplatform blend of policy nuance and number-crunching on Wonkblog, approached Katherine Weymouth, the Post's publisher, in recent weeks, the people said.

After consultation with the newspaper's editor, Marty Baron, according to one of the people, he put forward a proposal with detailed revenue projections to build a new website dedicated to explanatory journalism on a wide range of topics beyond political policy. It would have been affiliated with The Post, the person said, but would have been a separate enterprise. The investment he sought, the person said, was in eight figures.

Ms. Weymouth and the paper's owner, Jeff Bezos, declined to support the project. Since then, Mr. Klein has had discussions with several potential investors and venture capitalists in an effort to start the website himself, said those with knowledge of his plans, who insisted on anonymity in discussing them.

Though the atmosphere within The Post was described as civilized, one person said, there has been some awkwardness. Still, it is possible that Mr. Klein could remain at The Post if talks about his plans were rekindled.

As 2013 drew to a close, Neil Irwin, the economics editor of Wonkblog, joined The New York Times. Mr. Klein has been on vacation in San Francisco. Both declined to comment, as did The Washington Post.

The Washington Post owns the name Wonkblog, said a person with knowledge of the arrangement, and could continue it even without Mr. Klein.

News of Mr. Klein's proposal for a new website was first reported by The Huffington Post.

Several other journalists who had seen their brands grow at big media organizations have left to expand on their own. Nate Silver, widely lauded for the data analysis that led to his accurate prediction of the 2008 and 2012 presidential elections, left The Times in 2013 to build his own site, backed by ESPN. Walter S. Mossberg and Kara Swisher, who came to prominence at The Wall Street Journal with their AllThingsD technology reporting and conference business, announced in the fall they were striking out on their own. They secured minority investment, renamed their site ReCode, and left The Journal officially this week.

In an interview about that move earlier this week, Ms. Swisher said that they had decided against working in a large media company because "there is a lot of competition for resources, and there isn't always the same willingness to take risks."

Mr. Klein is also a policy analyst for MSNBC, where he sometimes fills in for other hosts, and he writes for Bloomberg View.