By Christmas 1978, the Landmark Center, Northern Virginia's oldest regional shopping center, plans to complete a $13 million expansion project that will include an enclosed mall, partially enclosed parking facilities, added sapce for two of its major department stores, and 29 additional small shops.

The expanded center is expected to contribute an additional $225,000 annually in real estate taxes to Alexandria's treasury, plus extra money in sales taxes and business license fees, according to Howard G. Glienke, manager of Landmark Center.

Glienke said the expansion is necessary because of population increases in the area surrounding Landmark. The shopping center is located in Alexandria at the intersection of Interstate Rte. I-95 and Duke Street.

"In the last seven years, they've built a number of condominiums," said Glienke, whose center is surrounded by what is known as condo canyon. "The population is growing westward in Alexandria (toward Landmark). They need additional services and retail facilities."

Glienke said that after construction is completed, the center expects a $35 million increase in sales. The center will still be smaller than Tysons Corner, which is 14 miles from Landmark, and the Springfield Mall, which is four miles away, Glienke said.

The planned expansion must be approved by Alexandria officials before construction can begin next spring. Glienke hopes to submit the plans in September and said that he expects "no obstacles" because he has already met with city and state officials. Expansion has been considered since 1973, he said.

Shoppers strolling through the new mall will find growing plants and skylight windows that will open and close as they adjust to the inside temperature. Glienke said architects and planners also are trying to determine if solar heat and lighting can be used.

The difference between the inside and outside temperatures will never vary more than 10 degrees "so you don't have the feeling of coming in from the cold and saying, 'whew, it's hot in here,' or coming in from the heat in the summer and catching cold from the air conditioning," Glienke said. Shoppers who park in the enclosed lot will not be exposed to rain or snow, he said.

Landmark now has 47 small stores, plus Sears, the Hecht Company, and Woodward and Lothrop. Woodie's will add 60,000 square feet to its store and Hecht's will add 65,000 square feet, according to plans. There will be an underground, environmentally controlled parking area with 663 spaces, with additional parking on two other levels. Glienke said. There also will be a new family restaurant.

Most of the 29 new stores will be those not at Springfield Mall or Tysons Corner, Glienke said. Currently, the three shopping centers share many small shops and boutiques.

Construction has been put off until next spring "because we don't want to discourage Christmas trade" this year, Glienke said. The $13 million construction cost will be shared by Woodie's Hecht Co. and Alexandria Partnership the developers, he said.

There are no plans for a Bloomingdale's or Lard and Taylor at Landmark Center, Glienke said.

"Most ot the families who shop at our stores are in the $16,000 to $20,000 income bracket," Glienke said. "We want the type of stores they can afford. They won't be cheap stores, but we're not going to price ourselves out of the market either. We want to give them a greater variety of selection."

Glienke noted that when Landmark was built 11 years ago, "it was literally out in the boondocks."

Because of inadequate transportation routes at that time, "it took a day's journey from downtown Alexandria to shop at Landmark," he added. With an expanded and improved I-95, the situation has changed drastically, he said.