Essentially all of the gains in part-time employment have been among people who are reluctantly working fewer hours because of slack business conditions for their employer or an inability to find a full-time job.

“It was a relief just to find something,” said Amie Crawford, 56, of Chicago. After four months looking for a new job as an interior designer, which she had been for 30 years before the recession, she accepted a position as a part-time cashier at a quick-service health-food cafe called Protein Bar.

She keeps asking for more hours, but her manager’s response is always the same.

“He tells me, ‘I try to give you as many hours as I can, but everybody wants as many hours as they can,’ ” Ms. Crawford said.

The owner of the company, Matt Matros, said that it was working on giving her more hours, but that each location had a limited need for cashiers. He added that Ms. Crawford had the opportunity to get trained in other skills if she wanted to advance or take on other positions.

Holding a part-time job when a full-time one is desired is frustrating for workers, and not only because fewer hours means less income. Like temp workers, part-timers are also less likely to get benefits and are more likely to be stuck with unpredictable schedules that make it hard to plan for child care, transportation or even a second part-time job.

“I’ll be on the schedule from this time to this time, so I expect to work from this time to this time,” Ms. Crawford said. “But because on a particular day, who knows, it’s snowing, raining, or people just didn’t come in today for whatever reason, they start cutting people. So I get sent home in the middle of my shift.”

Part-timers also generally earn less per hour than their full-time counterparts.

“The only remaining legal form of discrimination in the labor market is against part-time workers,” said John Schmitt, senior economist at the Center for Economic and Policy Research, a liberal research organization. “You can hire part-time workers and full-time workers doing the same job, and you’re allowed to pay them different money and different benefits.”