Caldor Inc., one of the nation's fastest growing and most successful discount chains, is coming to the Washington area by the end of this year.

The Connecticut-based 103-store chain has announced plans to open its first store in the metropolitan area on Route 1 in Alexandria in the newly named South Valley Center, which has been the home of the antique bazaar Thieves' Market.

The store should open by Nov. 1, and an additional three to five stores are planned for the area in 1986. Caldor already has seven stores in the Baltimore area.

"We intend to make the Baltimore-Washington market a very important market for us," said Caldor's chairman and chief executive, John M. Guinan. "We hope to have 12 to 15 stores, totally, in the area within the next two years."

Caldor likes to describe itself as the upscale discounter, selling brand-name clothing and appliances to middle- and upper-income customers at cut-rate prices. It is particularly known for its hard-line goods such as blenders, toasters, cameras and sporting equipment, which account for 70 percent of its business.

"Washington has a lot of demographics that make for a good Caldor customer," Guinan said. "Our customer tends to be an upscale suburban customer. There are plenty of those in Washington."

"Caldor is one of the best businesses in the country," said Monroe H. Greenstein, a financial analyst at Bear Stearns & Co. "They and Bradlees are the two best discounters in the Northeast."

"Caldor occupies the upscale niche of discount stores," noted Allan Pennington, president of the retail consulting firm Pennington Associates. "It is a significant notch above K mart Corp. and different than Bradlees, in that it has a stronger focus on hard goods. Bradlees has a stronger emphasis on soft goods" such as clothing and linens, Pennington noted.

Ringing up more than $1 billion in annual sales, Caldor is the fastest growing subsidiary of Associated Dry Goods, which owns a host of other retailing companies, including Lord & Taylor and Loehmann's Inc.

Caldor's entry here comes just two years after Bradlees opened 11 stores in the Washington area and just as K mart is trying to upgrade its stores and merchandise.

The first Caldor store in the Washington area will be in South Valley, which used to be called Hybla Valley Shopping Center. The developers who purchased the land last year initially planned to renovate the buildings but then concluded that a total redevelopment would be better and decided to rename the center as part of its make-over. The Outer World Limited Partnership will begin tearing down the Theives' Market this week. The antique bazaar will move into new quarters nearby.