Lord & Taylor, the big New York specialty chain, announced yesterday it will build its fourth Washington area store in a mammoth shopping center with six department stores planned for Fairfax City.

Lord & Taylor said it will join Woodward & Lothrop, Hecht's, Sears, Roebuck, J.C. Penney and an as yet unnamed retailer in the mall near the intersection of Interstate 66 and Route 50.

With almost 1.5 million square feet of stores, the mail will be the biggest shopping center in the Washington area, until the Tysons II project is built at Tysons Corner.

It will be built, starting this fall by the Taubman Companies, Inc., of Troy, Mich., which will open the Lakeforest Mail in Gaithersburg on Sept. 12.

Jumping the gun of Taubman, which planned to announce the Fairfax project next month, Lord & Taylor Chairman Joseph Brooks revealed his company's plans yesterday.

"The tremendous response and success we have achieved in the Washington market with our existing three stores has precipitated our further expansion in this area," Brooks said.

Lord & Taylor, he explained, will build a two-level store with 100,000 square feet of men's, women's and children's clothing as well as furniture and gifts.

Lord & Taylor has stores at White Flint, Seven Corners and on Western Avenue in Northwest Washington, where last year it completed a major remodeling.

Taubman apparently had been holding up announcing plans for the Fairfax project until the sixth anchor store is signed.

The giant mall will be on the 138-acre site of the Pinecrest Golf Course, an area that has long been designated on Fairfax County plans for retail development. Despite complaints that added traffic into the center would contribute to air pollution, Fairfax officials several months ago approved rezoning for the project.

In presentations to local governments, Taubman said the center would employ about 2,800 full-and part-time workers with a payroll of$18 million a year.