Plans for a new $15 million shopping center in St.Charles, Md., 35 miles south of Washington, were announced yesterday by Charles County officials and a Boston developer. At the same time it was announced that Almys department store, a Boston-based retailer, would be the anchor store of the 370,000-square-foot center.

The new mall represents the first third of what will eventually become a 2 million square foot center for the new community of St.Charles. A $6 million Holiday Inn is currently under construction next to the center. The developers, Wilder-Manley Associates, expect building to begin next spring.

For Almys, which will occupy 80,000 square feet, it marksthe first more into the mid-Atlantic area. The chain currently operates 32 outlets in New England and New York and has annual sale of $7 million. The move may bring Almys into head-to-head competition with two of the giants of retailing.

St.Charles lies approximately seven miles south of Mattawoman, a new town in Prince George's County at the intersection of Routes 301 and 5.J.C.Penny Co. and Montgomery Ward have announced they plan to open stores in a new mall to be built there. The companies have said they expect construction to begin next spring, but the date does not seem assured.

Zoning hearings over the question of sewage treatment facilities for the entire development are still going on this week