Grand Union Co. last week said it plans to pull out of the Richmond area and to close its eight Big Star supermarkets there.

About 375 employes will be laid off when the stores shut down in mid-December, said Kenneth A. Brown, vice president in charge of Grand Union's regional office in Landover.

Grand Union acquired the Big Star supermarkets when it bought Colonial Stores Inc. of Atlanta in 1978. A number of the Big Star units, including all those in the Norfolk area, have since been closed.

Last week's decision "is a withdrawal from Richmond, it is not a withdrawal from Virginia," said Don Valencourt, a spokesman at Grand Union's New Jersey headquarters.

Valencourt noted that the company recently expanded its operations in the Washington suburbs by opening a Basics discount food store in Woodbridge, the eighth Basics unit in the area. Last month, also in Woodbridge, the company opened its second expanded Grand Union Food Market in this area. The stores are an amplified version of a regular Grand Union, with fresh seafood, a bakery, a natural foods section and enlarged deli, meat, and produce sections.

Brown said the Richmond stores will be closed because they were "not operating satisfactorily" and efforts to boost business had failed. In addition, he said, the stores' union contracts required them to pay higher wages than non-union independent supermarkets in the Richmond area.

Grand Union announced that all groceries at the Richmond Big Star stores will immediately be marked down 20 percent, and the stores would close when inventories are depleted.

Brown said Grand Union auctioned the store properties.