Mars Super Markets Inc. has begun construction on an expansion project that will add about 15,000 square feet to a former Valu Food store in the St. John's Plaza shopping center in Ellicott City.

Demolition of an exterior wall of the building began about a month ago, according to the construction project manager. The company will install new piping and wiring to handle the modern equipment it plans to use in the store.

At a planned 45,000 square feet, the Mars store will be mid-size compared with several other supermarkets along the U.S. 40 corridor. The family-owned company has 16 stores in Maryland. The Ellicott City location will be its first in Howard County.

"On the plus side, Mars certainly has a clear point of difference in that it's family owned and there's more of a priority on customer service," said Jeff Metzger, publisher of Food World, a grocery trade magazine. "They bring a mix the others retailers don't."

But the company will face challenges in what Metzger considers an overcrowded market place.

"That marketing area is significantly over-stored," Metzger said. "[There are] too many stores to serve the population, especially when you throw in the Wal-Mart [about a mile east, off U.S. 40] and the Target at Long Gate [shopping center], which is generally the same marketing area."

Mars officials did not return phone calls seeking comment.

Mars is not the only grocer planning to expand. A spokesman for Giant Food Inc. said the company wants to put a prototype store at the site of its next new outlet - in a shopping center along Route 108, where the closed Palace 9 movie theater stands.

Giant is awaiting county permit approval to build a store of between 55,000 and 60,000 square feet in the Columbia 100 Office Research Park, said Barry Scher, a vice president and spokesman for the company.

The store will be part of an aggressive building and renovation program, and it will offer a glimpse of things to come from Giant. The company has planned several major renovations and a store opening each month of next year, he said.

"It'll have a lot of prepared foods [and] it'll be a little larger than some of the stores we have built," Scher said. "It'll be the latest in merchandising trends."

Construction is scheduled to begin early next year, he said, with an expected opening date before the end of next year. In addition to being part of a growth campaign, the store will be the company's effort to keep Safeway and other retailers at bay. Giant is a leading retailer in the county, having stores in five of Columbia's nine villages. A renovation at the store in Owen Brown village was completed last week, which added 21,000 square feet, bringing it to 60,000 square feet.

Giant also broke ground this fall on a 368,000-square-foot fresh-food distribution facility in Jessup, for which it received $2 million in incentives, including $225,000 from the county for road improvements.

But Safeway is a close competitor, especially in east Columbia, where it has two stores around Giant's new location, including a store in Long Reach Village Center that was remodeled and expanded a few years ago and a store in the Long Gate shopping center.