Steven Greenhouse

SPRING VALLEY, CALIF.: Since the Fresh & Easy grocery chain was founded five years ago, it has opened 150 markets in California and positioned itself as a hip, socially responsible company.

A cross between Whole Foods and Trader Joe’s, the company brags that its house brands have no artificial colors or trans fats, that two-thirds of its produce is grown locally and that its main distribution center is powered by a $13 million solar installation.

But in one crucial respect, Fresh & Easy is just like the vast majority of large American retailers: Most employees work part time, with its stores changing many of their workers’ schedules week to week.

At its store in Spring Valley near San Diego, Shannon Hardin oversees seven self-checkout stations, usually by herself. Typically working shifts of five or six hours, she hops between stations — bagging groceries, approving alcohol purchases, explaining the checkout system to shoppers and urging customers to join the retailer’s loyalty program, all while watching for shoplifters.

“I like it. I’m a people person,” said Hardin, 50, who used to work as an office assistant at a construction company until times went bad.

But after nearly five years at Fresh & Easy, she remains a part-time worker despite her desire to work full time. In fact, all 22 employees at her store are part time, except for the five managers.

She earns $10.90 an hour, and with workweeks averaging 28 hours, her yearly pay equals $16,500. “I can’t live on this,” said Hardin, who is single. “It’s almost impossible.”

While there have always been part-time workers, especially at restaurants and retailers, employers today rely on them far more than before as they seek to cut costs and align staffing to customer traffic. This trend has frustrated millions of Americans who want to work full time, reducing their pay and benefits.

“Over the past two decades, many major retailers went from a quotient of 70 to 80 percent full-time to at least 70 percent part-time across the industry,” said Burt P. Flickinger III, managing director of the Strategic Resource Group, a retail consulting firm.

No one has collected detailed data on part-time workers at the nation’s major retailers. The Bureau of Labor Statistics, however, has found that the retail and wholesale sector, with a total of 18.6 million jobs, has cut 1 million full-time jobs since 2006, while adding more than 500,000 part-time jobs.

Technology is speeding this transformation. In the past, part-timers might work the same schedule of four- or five-hour shifts every week. But workers’ schedules have become far less predictable and stable. Many retailers now use sophisticated software that tracks the flow of customers, allowing managers to assign just enough employees to handle the anticipated demand.

“Many employers now schedule shifts as short as two or three hours, while historically they may have scheduled eight-hour shifts,” said David Ossip, founder of Dayforce, a producer of scheduling software used by chains like Aeropostale and Pier 1 Imports.

Some employers even ask workers to come in at the last minute, and the workers risk losing their jobs or receiving fewer hours in the future if they are unavailable.

The widening use of part-timers has been a bane to many workers, pushing many into poverty and forcing some onto food stamps and Medicaid. And with work schedules that change week to week, workers can find it hard to arrange child care, attend college or hold a second job.

Many people prefer to work part time — for instance, college students eager for extra spending money and older people who work during the holiday season to earn money for gifts. But in two leading industries — retailing and hospitality — the number of part-timers who would prefer to work full time has jumped to 3.1 million, or 2˝ times the 2006 level, according to the Bureau of Labor Statistics.