LONDON – Tesco, the large British grocery retailer, disclosed Monday that it had overstated its expected half-year profit by about $400 million and that it had suspended four senior executives.

The accounting irregularity will add to the struggles of Tesco, which has been battered by earnings downgrades and leadership turnover. Once a dominant food retailer in Britain, the company has lost ground to discounters.

Dave Lewis, the company's new chief executive, said he became aware of the accounting problem Friday when an employee brought it to the company's attention. Lewis suggested that the problem involved incorrect reporting of the timing of payments to Tesco from suppliers for things like product promotions.

"We have uncovered a serious issue and have responded accordingly," Lewis said. "We will take decisive action as the results of the investigation become clear."

Tesco said Monday that it believed the guidance it had given markets last month for the six-month period through Aug. 23 was overstated by an estimated $409 million.

The company said on a call with analysts that it had put its e-commerce head, Robin Terrell, in charge of British operations while outside auditors investigated its accounts. Terrell is taking on a role that had been held by Chris Bush.

Lewis, a former Unilever executive, took the helm of Tesco at the beginning of this month. He was supposed to begin on Oct. 1 but his predecessor, Philip Clarke, whose removal was announced after a profit warning in July, left earlier than expected.

NEW YORK TIMES