WHEN CHEF ERIC Greenspan opened the Foundry, a $1.3 million restaurant in Los Angeles, two years ago, he created a menu of high-end cuisine, showcasing the culinary skills he had honed at some of the world's top restaurants. Three months ago, Mr. Greenspan turned the restaurant into a lounge with nightly live bands, cocktail waitresses and promotions such as "fried-chicken-and-waffles night." The dining room has been banished to a back patio.

"The lounge is keeping us alive," he says.

Around the country, proprietors are turning their restaurants – or significant parts of them – into glorified bars. They're ripping out dining-room tables to make more bar space, applying for late-night and cabaret licenses and adding the word "bar" to their names. Top chefs are serving up bar snacks like grilled cheese sandwiches and hot dogs.

The reason: While consumer spending at restaurants is falling precipitously, drink orders, particularly for cheaper drinks like beer, are barely dropping off. For restaurants, it's now proving more cost-effective to serve lower-priced dishes that diners can munch on as they buy drinks.

Alain Ducasse's Benoit bistro in New York recently rolled out a bar menu that includes sliders and $1 deviled eggs. Daniel Boulud, the Manhattan chef behind one of the city's most formal restaurants, Daniel, plans to open DBGB Kitchen & Bar, featuring 24 beers on tap and homemade sausage and hot dogs, in May or June. Christophe Ém, chef and owner of Ortolan in Los Angeles, has begun calling about 100 customers a week to tell them about his new bar menu.

Even Thomas Keller's Per Se restaurant in Manhattan, where the only dinner option has been a $275, nine-course prix fixe menu, launched an a la carte menu for its lounge area last week. Unlike the main dining room, where dinner tables typically book up two months in advance, the lounge doesn't take reservations. Diners are seated around coffee tables.

Per Se's a la carte menu is pricey by most standards – a small entre of white polenta agnolotti in a green garlic sauce is $28 and a slab of sauted foie gras with sunchokes and watercress is $40 – but diners can spend far less than they would on the prix fixe. On a recent night, the restaurant also offered diners complimentary tastes of signature items such as gougres and salmon cornets. The bar tab can add up quickly: Red wine by the glass starts at $19 and runs as high as $40.

The morphing of some of the nation's top dining rooms into bars and lounges with food demonstrates how dramatically and quickly consumer behavior has changed since the economy plummeted this fall. Technomic, a Chicago restaurant consultant, predicts that this year fine dining sales will plunge at least 12%, after falling 4% last year.

Meanwhile, analysts are predicting a less painful contraction in alcohol sales: Technomic predicts a 1.6% decline in sales of alcohol consumed where it is sold.

"Historically, consumption of alcohol tends to outperform compared to other parts of the economy in a recession," says Brian Sudano, managing director of BMC Strategic Associates, a New York consultant to the beverage industry.

Selling alcohol, and cocktails in particular, is typically a better business than selling restaurant food because the margins are higher. While ingredient costs may account for as much as 35% of the price of an entre in a high-end restaurant, they typically only account for about 14% of the price of a cocktail or 25% of the price of a glass of wine.

Bar snacks, which often include inexpensive items like pizzas, can also have better margins than fine-dining dishes with expensive proteins such as filet mignon or organic lamb. Since restaurants are already paying to run a kitchen, selling additional, easy-to-make food is simply an extra revenue stream.

Beyond thrift, there is a social component to noshing at bars. Restaurateurs say patrons seem especially eager to rub shoulders with one another at the bar, rather than isolate themselves at dining-room tables.

"People want to socialize and be out; they don't want to be miserable at home," says Chris Douglass, co-owner of three Boston-area restaurants, including the 32-year-old fine-dining restaurant Icarus, which Mr. Douglass says he would like to either sell or turn into a "gastropub" – a bar that serves high-quality food – if he can find buyers or investors.

Seven weeks ago, he began beefing up the bar scene in his seven-month-old Boston restaurant Tavolo, by applying for a late-night license that would allow him to stay open two hours later, until 1 a.m., as well as an entertainment license, which means he could have a DJ. He also ordered three more taps in order to serve more draft beer.

Last Thursday, friends Kat Garcia, a 27-year-old television publicist, and Quinn Doan, 34, a hotel publicist, sat perched on stools in the bar area of L.A.'s Ortolan. Over the course of the evening, they spent about $150 including tax and tip, on wine, Champagne, four appetizers and two desserts – about $100 less than what a meal in the dining room might have cost. Ortolan's bar-only dishes include langoustine ravioli in consomm for $9, compared with $19 to $25 for appetizers and roughly $40 for entres on the dining-room menu.

"You could go to any other place and buy a $7 to $10 appetizer and you might get a bowl of fries," Ms. Garcia said.

Both the restaurant and bar area were nearly empty at 7:30 p.m. Mr. Em says the restaurant's drop-off in traffic spurred him to roll out the bar menu, which he says is still getting off the ground.

The same night at 8 p.m., the Foundry was over a third full, mostly with patrons in their 20s and 30s. The bartender cheerfully made small talk with customers and Mr. Greenspan, the chef, worked the room. The bar and the lounge tables all sported peculiar glass tanks with spigots. A hostess explained the contraptions were for dripping water onto a sugar cube placed on a spoon over a glass of absinthe; an absinthe company had sponsored the jazz music that night.

Informal dining is increasingly popular, and some of the restaurants launching bar menus and lounges will likely keep them even after the economy bounces back. But when consumer spending loosens up, Mr. Greenspan plans to convert the Foundry back into a regular restaurant, he says.

"I want to be able to go back to what I am known for and what I do really well," Mr. Greenspan says.

Write to Katy McLaughlin at katy.mclaughlin@wsj.com