In a bid to become Washington's dominent discounter, the Woolco division of F.W. Woolworth Co. will open five more discount stores in the Washington area this summer.

Woolworth and Giant Food announced yesterday that Woolco will move into three of the four Giant Department Stores that closed last week. Woolco will take over the Giant stores at Tysons Corner, Rockville and Bowie.

A month ago Woolco agreed to sub-lease two former Dart Home stores in Rolling Valley Mall, Burke, and Manaport Plaza in Manassas.

The five new units will give Woolco 12 stores scattered around the belt-way, more than any other discount chain.

Woolworth officials said the new stores are expected to produce at least $35 million a year in additional business, boosting Woolco's share of the market into the $75 million to $100 million range.

Woolworth said it will remodel and reopen all five stores this summer, but does not yet know whether the five will debut as group.

Woolco's agreement in principle to lease the three Giant stores was announced only a week after Giant ended going-out-of-business sales for its discount store operation, which produced $40 million a year sales but lose money in the latest year.

Even with its strong position in the Washington food market, Giant could not compete with the national discount chains, the company said when it decided in late December to close the stores.

Taking over the five additional stores will make Washington one of the top markets for Woolco, which has adopted a strategy of clustering stores in major markets for maximum advertising and operational efficiency.

Giant said it will continue to operate the food and pharmacy departments in the Rockville store. The company said it is still negotiating to lease the fourth vacant store, in Landham, and plans to keep its food store there.

Woolco will buy the store fixtures along with taking over lease in the three Giant stores.

The units being taken over from Dart were separate Dart Home stores, which were consolidated with adjoining Dart Drug Stores.

An F.W. Woolworth spokesman said the company anticipated "sales substantially in excess of $100 a square foot" from the new stores. The Manassas Dart store has 55,000 square feet of selling area, and the Burke store 58,000 square feet. The selling space of the former Giant stores is 97,000 square feet at Tysons Corner, 80,000 at Rockville and 68,000 square feet at Bowie.

The stores are somewhat smaller than most of those being built from the ground up by Woolco, which average 90,000 feet of selling space.