Sprint Nextel, the troubled No. 3 wireless carrier, lost nearly a million customers in the second quarter. But the company says it lost some of them on purpose.

Meanwhile its chief rivals, AT&T and Verizon Wireless, respectively gained 1.3 million and 1.5 million new wireless customers. As customers tighten their spending during rough economic times and when nearly nine out of every 10 Americans already own a cellphone, winning customers from a competitor is the only way to grow quickly. And at that task, analysts say, Sprint is struggling.

Daniel R. Hesse, who has been chief executive of the company since January, said that Sprint had deliberately rid itself of some of those 901,000 customers. Mr. Hesse said Sprint tightened credit standards in order to focus on keeping dependable mobile phone customers who have the money to pay their monthly bills. “We did it knowingly,” he said. “We are interested in quality, not quantity.” Sprint said Wednesday that it now has 51.9 million customers.

Mr. Hesse, who appears in ads for Sprint, said the failure to attract new customers was because customers did not know that Sprint had improved.