The hottest trend this decade in shopping-center development has gone cold.

Known as lifestyle centers, the open-air shopping venues offer small parks, fountains and cafés amid name-brand retailers selling fashion apparel, housewares and other discretionary fare. Developers raced to add new ones as they became popular with shoppers, especially women between 20 and 50 years old, a coveted category. Meantime, construction of traditional enclosed malls all but stopped.

Kris Hudson/WSJ A Cedar Hill, Texas, lifestyle center is only half occupied. The storefront in back remains vacant.

But now, with the economy slumping and shoppers spending less, retailers that had flocked to the centers -- like Chico's FAS Inc., AnnTaylor Stores Corp. and Talbots Inc. -- have begun canceling expansion plans and even shutting stores. Others, such as Linens 'n Things Inc., have sought bankruptcy protection.

This couldn't happen at a worse time for lifestyle-center developers, which were putting up more of the shopping centers than ever. Last year they built 37 centers totaling some 12 million square feet, or roughly 40% of the total lifestyle-center square footage added this decade, according to market-research firm Portfolio & Property Research Inc. Double the 2007 total is now under construction, and three times as much is in the planning stages.

The economic slowdown, of course, means many of the planned projects won't leave the drawing board. But many centers where constuction has begun will probably have difficulty leasing space when they open. That raises the specter that eventually they may not be able to pay their debt, adding to the strain on the already ravaged finance sector.

Leasing problems have clearly begun. Developer M.G. Herring Group opened its Uptown Village regional lifestyle center in the Dallas suburb of Cedar Hill in March with only half of the space occupied and the rest walled off with wood panels bearing the center's marketing images. President Gar Herring says he has so far signed retailers for 60% to 70% of the 725,000-square-foot project, though it remains only half occupied five months after its opening.

Kris Hudson/WSJ The small-shop space at Prairie Center shopping center in Brighton, Colo., is mostly empty.

In Brighton, Colo., THF Realty Inc. has filled most of its new Prairie Center retail project with such big-box retailers as Dick's Sporting Goods Inc. and PetSmart Inc. But Prairie Center's small-shop space -- erected in a lifestyle-center format nearby -- is mostly empty. Half-a-dozen tenants, including Heidi's Deli, Verizon Wireless and Elite Nails, are sprinkled among vacant storefronts sporting "for lease" signs.

Herring and THF executives say they anticipate no difficulties paying their debt service on the projects.

Some believe that the lifestyle-center craze was about to run its course in any case. The metropolitan locations that are best suited to the centers are mostly taken. "There were a number of projects proposed in markets that didn't really have the [sales] demand to support the projects," says Stephen Lebovitz, president of mall owner CBL & Associates Properties Inc., which has built two open-air centers.

Certainly the centers being built now show an evolution in the approach to the centers. Recent versions have larger formats and more diverse tenant rosters, including department stores and movie theaters. Few developers now propose the original format, which offers only small shops and spans 200,000 square feet or less. "Those are dead," says Maury Levin, a retail-property broker at commercial real-estate firm KLNB Inc. in Baltimore.

Construction of other retail-property formats is also slowing as consumer spending wanes. Portfolio & Property Research forecasts that in 2009, retail-space construction in the top 54 U.S. markets will drop 48%, to 71 million square feet, from this year. Existing properties are hurting, too. Vacancy rates at U.S. malls and shopping centers have climbed to 7.4% this year, the highest level this decade, according to market-research firm Reis Inc.

Many developers that have the option are canceling or scaling back projects. Citing slow progress in leasing, Opus Corp. opted to proceed in phases at a lifestyle center in the Seattle suburb of Issaquah, Wash., scheduling the opening of 150,000 square feet of shops in 2010. It had planned to open three times as much space in 2009.

In Canonsburg, Pa., developer Cullinan Properties Ltd. has delayed by a year, to 2010, the opening of 200,000 square feet of small shops intended to accompany a 14-screen movie theater as it struggles to lease the space.

What's tripping up many developers is the tendency of lifestyle-center tenants to travel in packs. The centers often don't have big anchor stores, so many retailers insist that several complementary stores agree to open in a given center before they will do so. "You may have 10 tenants you want to get, but eight are waiting until the fall to make a decision and the other two are waiting on those eight," says Frank Natanek, Cullinan's group president of real estate and marketing.

Poag & McEwen Lifestyle Centers LLC, which has developed 10 lifestyle centers, recently scrapped plans for one in Boise, Idaho, after five retailers reneged on signing leases there and then several more did the same. The Memphis, Tenn.-based developer proceeded with construction of a lifestyle center in Plainfield, Ill., only after tenants there waived the requirement that certain fellow retailers such as Chico's join the project. Chico's has pared its expansion markedly to 45 new stores this year from 118 last year.

Despite these stresses, most new lifestyle centers aren't in danger of immediate foreclosure. Developers and lenders typically structure construction loans to carry fledgling projects through lease-up periods, and they're hoping that the economy will rebound by the time those reserves are depleted.

"You're not really going to see these projects get turned over to the lenders until later this year at the earliest," says Ben Yang, an analyst with Green Street Advisors.

Write to Kris Hudson at kris.hudson@wsj.com

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