McDonald's has always had skeptical customers like Sylvia Mercer, who suspected that its mass-produced burgers were sunning too long under the heat lamp.

"It was like they were left from the morning," the Fort Washington resident said as she walked into the McDonald's off Brentwood Parkway in the District.

Now, however, the familiar heated storage bins are vanishing at McDonald's restaurants across the nation. And after 44 years of making us have it their way, McDonald's is making sandwiches one by one in its new made-for-you system.

In a shameless aping of Burger King's Have-It-Your-Way program, McDonald's is launching a process that allows it to assemble the sandwiches after customers make their decisions. And they pledge that patties will not be hanging around too long after they're cooked.

Under the old method, McDonald's burgers were cooked, assembled, wrapped and then kept in a heated area close to the counter. That meant customers had to pick off unwanted pickles or wait a few minutes for a special-order burger. Now, "they're getting the food made exactly for them," said Faith Krebs, operations director for McDonald's restaurants in the Washington area. "It's hot and fresh, and has all the condiments that they want."

The cultural shift taking place in McDonald's restaurants across the nation is a significant move for the mature chain. By far the largest fast-food operator, with $36 billion in systemwide sales last year, McDonald's is looking for ways to increase its revenue in the United States, where it is nearing the saturation point. At the same time, it wants to defend its turf from a growing pack of rivals.

"I think McDonald's always feels that everyone is nipping at its heels," said Don DeBolt, president of the International Franchise Association.

By improving the quality of its food, McDonald's also may be able to lure families who recently have opted to dig deeper into their wallets and dine at more upscale restaurants, DeBolt said.

"In an affluent period like this, there's a trade-up aspect to dining out," he said. "People who went to McDonald's may go to Ruby Tuesday."

There's some evidence that McDonald's may be sacrificing speed in its quest for fresher food, or at least until employees adjust to the made-for-you way of doing things.

John Dorsey, a District retiree who frequently dines at McDonald's, says he has been pleased with most of the changes. The stores seems brighter and the food looks fresher. "The only thing is it takes a little bit longer," he said.

McDonald's initially announced it would switch to the made-for-you system in 1997. But revamping all 12,500 stores has been a daunting task. Locally, the renovations only began last summer, with the company paying for changes to its stores and franchisees picking up the tab in their stores.

The overhauled stores now feature high-tech toasters that can brown buns in 11 seconds. New heated holding cabinets sound alarms after hamburger patties have been around too long. Restaurants must toss them out after a certain time, which McDonald's officials would not disclose.

McDonald's also has introduced video screens next to the drive-through menus that allow customers to review orders and the total bill before picking up their food.

Although Burger King was first, McDonald's may have moved one step ahead of its rivals, industry experts said.

"Burger King has had the have-it-your-way system for a long time, so they have been able to argue that they've done it," said Ron Paul, president of the restaurant consulting company Technomic Inc. "But McDonald's now has more technologically advanced equipment."

Not for long, said Kim Miller, a spokeswoman for Burger King Corp. of Miami.

Burger King, the No. 2 fast-food operator, with 8,000 restaurants nationwide, is revamping its restaurants in Orlando to add "variable speed broilers" that can cook several products simultaneously. And they will have toasters that can brown buns in eight seconds.

Burger King plans to redo all 43 restaurants in its Orlando market by next spring and then will expand the effort to other markets, she said.

McDonald's already has lined up its franchisees, however. And the investment is sizable. The new kitchen equipment and other improvements can cost more than $100,000 per store.

Several franchisees say they were willing to open their own wallets because the new systems allow them to expand their menus. The new kitchen equipment also promises to cut food costs, local operators said.

"Previously, we'd prepare based on what our sales trends had been in the past," said Bob Alvarez, owner of the McDonald's restaurant off Brentwood Parkway. "If we had a slow day, we'd have more waste. Now, [the new system] makes waste unnecessary or even impossible."

Customers and employees alike are cheering the new video screens by the drive-through. Solved are some of McDonald's biggest drive-through problems: botched orders after car passengers changed their minds or talked over each other.

"You don't know who changed what," said Max Van Valkenberg, whose family owns 19 McDonald's restaurants in Northern Virginia and the District, said, "Now the customer can see [the order]. It makes the customer experience much more satisfying."