In the first sizable layoffs in its history, Google is cutting about 300 jobs from the American operations of DoubleClick, the advertising technology company that it acquired recently, according to a person with direct knowledge of Google’s plans.

The cuts represent about a quarter of DoubleClick’s American work force of about 1,200. The company has about 1,500 employees worldwide, and the chief executive of Google, Eric E. Schmidt, has suggested that job cuts would also affect DoubleClick’s overseas operations at a later date.

Google declined to confirm the number of layoffs.

In a statement, the company said: “Since our acquisition of DoubleClick closed on March 11, we have been working to match and align DoubleClick employees in the U.S. with our organizational plan for the business. As with many mergers, this review has resulted in a reduction in headcount at the acquired company.”

Google said it also planned to sell a DoubleClick unit, Performics Search Marketing, that helps marketers place ads on search engines, including those owned by Google and its main rivals, Yahoo and Microsoft.