ConAgra Foods Inc. CEO Sean Connolly, after only three months on the job, is undoing the company’s $6.7 billion acquisition of private-label food maker Ralcorp amid pressure from an activist investor.

The business, which makes products under supermarkets’ names, is being sold because turning it around represents a “suboptimal use” of ConAgra’s resources, Connolly said in a statement Tuesday. The company will release operating details of its plans and long-term financial expectations at an investor event later this year, he said.

ConAgra has struggled with slumping sales and profit ­following the 2013 acquisition of Ralcorp, hurt by management missteps and an ­overreliance on products in struggling categories. Jana Partners, a hedge fund founded by Barry Rosenstein, disclosed a 7.2 percent stake in ConAgra this month and threatened to nominate three directors.

“This will give them more time and energy to focus on their better-performing ­businesses,” said Michael Halen, an analyst for Bloomberg Intelligence. Still, shareholders will see some value destruction because they won’t get what they paid for it in 2013, Halen said.

Given the division’s lackluster performance, it’s a likely target for private-equity ­buyers rather than another food company, Halen said.

ConAgra rose 0.7 percent to close at $43.72 in New York. The Omaha-based company has gained 21 percent this year, with much of the gain coming after Jana’s stake was disclosed.

Jana has said it started amassing the stake after ConAgra wrote down the Ralcorp deal by $1.3 billion in March. Before the ­Ralcorp acquisition, ConAgra was focused on packaged foods with well-known brand names. Its lineup includes Chef Boyardee, Healthy Choice brands, Hunt’s ketchup, Swiss Miss and Orville ­Redenbacher.

The deal was a bet that Ralcorp’s faster-growing private- label business would be a good fit for the company. Instead, ConAgra struggled to ­combine the two businesses, cutting the sales force too much and reducing prices, which ate into margins, Halen said.