Raleigh Stores Corp. yesterday opened its 11th and most unusual store at White Flint Mall on Rockville Pike. The Ralieghs branch features men's and women's apparel and is the third largest store in the shopping center - behind Bloomingdale's and Lord & Taylor.

The modernistic store, on four levels, was designed by the New York firm of Copeland/Novack/Israel. It features burnished copper, steel, glass and mirrors with angular, suede-like covered walls.

A centerpiece is a reflective atrium that permits visual access to merchandise on all four levels of the 28,000-square-foot retail location. A company spokesman said last night that the store had experienced an 'active day,' with good consumer traffic.

In the near future, a copper-wrapped circular elevator will be in operation, connecting the four interior levels. Raleighs itself opens to White Flint Mall at two levels.

"All stops were pulled out to make this the most beautiful Raleighs to date," said Raleigh president Sidney Lansburgh Jr. yesterday. The furnishings are the cost expensive that Raleighs has installed in a store and the total investment was more than $1 million.

The 66-year-old Washington retail chain has devoted nearly 10,000 square feet to women's apparel at White Flint: some two-thirds of the company's volume is in menswear.