Wal-Mart Stores Inc., the largest private employer in America, is expanding the number of health care plans it offers employees and giving discounts on some types of coverage in an effort to blunt criticism about benefits.

American workers will also be able to pay $4 for a month’s supply of any of 2,400 generic prescription drugs, saving them $25 million next year, the company said yesterday. Those who enroll in Wal-Mart’s Value Plan, introduced last year, will receive a credit of $100, $250, or $500 for each covered family member.

Labor and political leaders have criticized Wal-Mart’s health plans for being too expensive and supported legislation to mandate certain benefits. Last year, the world’s largest retailer shortened wait times to enroll in health coverage and started offering family plans to part-time workers.

“It’s a marked improvement from Wal-Mart’s previous plan,” a spokesman for the advocacy group Wal-Mart Watch, Nu Wexler, which generally is critical of the Bentonville, Ark.-based retailer. Health-care costs “remain a huge burden” for Wal-Mart employees, Mr. Wexler said.

Wal-Mart Watch, based in Washington, is a coalition of labor, environmental, religious, and community groups.

Company spokeswoman Sarah Clark said the $25 million in employee savings from the generic drug plan was a “conservative” estimate and based on the number of generics used by workers or their families today.

Wal-Mart a year ago started selling a month’s supply of some common generic drugs for $4 after offering workers $3 prescriptions on about 20 generics. Wal-Mart rolled out the $4 retail program, which now includes 331 items, at all its pharmacies in November.

With almost 1.4 million full-and part-time workers in America, Wal-Mart has been criticized for offering stingy benefits and in some communities faced efforts to legislate what it pays for employees’ health care.

In July 2006, a federal judge overturned a Maryland law that required large companies, in particular Wal-Mart, to spend at least 8% of payroll on health benefits. The same month, the mayor of Chicago, Richard Daley, vetoed a city ordinance that would have required certain retailers, including Wal-Mart, to increase their minimum wage.

The chief executive officer, H. Lee Scott, has joined with two labor unions and other corporations in calling for an overhaul of the American health-care system that would guarantee universal coverage by 2012. He’s working with the president of the Service Employees International Union, Andrew Stern, a frequent critic of the company and chairman of the board of Wal-Mart Watch.