To keep up with its critics, Wal-Mart "has to run a campaign," said Robert McAdam, a former political strategist at the Tobacco Institute who now oversees Wal-Mart's corporate communications. "It's simply nonsense for us to let some of these attacks go without a response."

Wal-Mart's aggressive new posture is a departure from its tradition of relying on an internal staff to manage the company's image. The war room, which is part of a larger Wal-Mart effort to portray itself as more worker-friendly and environmentally conscious, runs counter to the philosophy of the chain's founder, Sam Walton. Believing that public relations was a waste of time and money, the penny-pinching Mr. Walton would not likely have hired a public relations firm like Edelman, Wal-Mart's choice to operate its war room.

So what has changed? For one thing, Wal-Mart's critics have become more sophisticated.

For years, unions hurled little more than insults at the chain. But over the last year, two small groups -- Wal-Mart Watch and Wake Up Wal-Mart -- set up shop in Washington with the goal of waging the public relations equivalent of guerilla warfare against the company. Wal-Mart Watch received start-up cash from the Service Employees International Union; Wake Up Wal-Mart is a project of the United Food and Commercial Workers International Union. Unions have tried, unsuccessfully, to organize Wal-Mart's employees.

At the suggestion of Wake Up Wal-Mart, members of the nation's largest teachers' unions staged a boycott of Wal-Mart for back-to-school supplies this fall. Wal-Mart Watch, meanwhile, set up an automated phone system that called 10,000 people in Arkansas in June seeking potential whistle-blowers willing to share secrets about the retailer.

Wal-Mart did not rebut such attacks, even when Wal-Mart Watch released a 24-page report blasting the company's wages and benefits. Wal-Mart Watch said the report had been downloaded from its Web site 55,000 times.

Once a darling of Wall Street, Wal-Mart's stock price has fallen 27 percent since 2000, when H. Lee Scott Jr. became chief executive, a drop that executives have said reflects, in part, investors' anxieties about the company's image. Sales growth at stores open for more than a year has slowed to an average of 3.5 percent a month this year, compared with 6.3 percent at Target. And Wal-Mart is facing growing resistance to new urban stores, with high- profile defeats in Los Angeles, Chicago and New York.

There is some evidence that criticism is influencing consumers. A confidential 2004 report prepared by McKinsey & Company for Wal-Mart, and made public by Wal-Mart Watch, found that 2 percent to 8 percent of Wal-Mart consumers surveyed have ceased shopping at the chain because of "negative press they have heard."