The United Way of America is undertaking a major expansion of its national headquarters in Alexandria.

The plan, which has been approved by the association's board of governors, is to build a 120,000 square foot office and training center at a cost of $4 million on a two-acre site next to United Way's current headquarters at 801 N. Fairfax St. That building was recently sold for $6.5 million to Mr. and Mrs. Khaled T. al Ghanem. United Way will lease the building for two years while the new faciltiy is under construction. United Way will also sell a nearby vacant parcel of land.

The decision to expand was based on a study of a special committee led by John R. Opel, president of Interantional Business Machines. The study found that United Way would require 60,000 additonal square feet of space over the next 10 years.

"In additon to providing expanded services to the 2,200 local United Ways, United Way of America's new facility will be designed to offer training and technical assistance to staffs and volunteers of other charitable organizations," said William Aramony, Untied Way of America national executive.

Already more than $2 million has been committed by corporations and labor unions to pay for the building. Contributions to local United Ways will not be used for the building.