In one big splash, Bradlees Department Stores is hoping to make waves in the Washington retail market with Thursday's official opening of 10 stores.

Forming a ring along the Beltway in renovated former Memco stores, the Boston-based chain is aiming to fill the shopping gap left by the closings of Memco, Woolco and Korvettes and capture $100 million a year in retail business.

Bradlees' spokeswoman said the stores will conduct a "soft opening" today for holders of the now-defunct Memco stores' membership cards, and then open to the general public Thursday.

Bradlees will also open a store this week in Richmond and another in Burke in November.

Considered an upscale retail discounter, Bradlees stores fall somewhere between Garfinckel's and Woodward & Lothrop department stores and K mart and Zayre discounters. The company expects its new stores to meet the chain-wide average of about $9.1 million a year in sales.

Sales for Bradlees, a subsidiary of the Stop and Shop Companies Inc., topped $871.6 million last year. Company executives predicted they will reach $1 billion this year.

The chain has been expanding south from New England for the past several years. It started a big push last year with the opening of 12 stores in New Jersey and upstate New York.

With the opening of these stores--the single largest opening in the company's history and probably the biggest single move into the Washington area--the total number of Bradlees stores will climb to 123. The discounter intends to open a total of 20 new stores in 1983 and eight to 10 stores every year for the next few years, company officials said.