A Netherlands corporation, B.V. Cofintab, has purchased 4.6 percent of the stock of Federal Realty Investment Trust and says it may acquire additional shares through an agreement with another Dutch firm that is Federal REIT's biggest stockholder.

Federal Realty president Steven J. Guttman said the trust sold 300,000 shares of new stock to Cofintab in a private placement sale negotiated late Thursday. Announcement of the sale was delayed until yesterday because of the weather.

Cofintab, a subsidiary of a Dutch tobacco firm, agreed to pay $4.24 million for the stock, based on a price of 50 cents a share above the recent market price of about $13 5/8.

Cofintab's purchases represent about 4.6 percent of Federal Realty's more than 5.7 million shares. The largest stockholder in Federal REIT is SIAM Ltd., a Netherlands plantation company, which now owns 8.8 percent of the stock.

Cofintab and SIAM are not related companies, but executives of the two Dutch firms "are acquainted with each other" and SIAM suggested that Cofintab invest in Federal Realty, said Philip S. Smith, vice president-finance.

Guttman said the transaction "solidifies a continuing relationship with SIAM." As part of the stock sale, SIAM and Cofintab signed a 10-year "standstill agreement" with Federal REIT, he said.

Cofintab and SIAM will not increase their combined holdings to more than 16 percent and will vote their stock in favor of the management's nominees for the board of directors for the next five years.