GAF <GAF> TO PURCHASE UP TO 21 PCT OF STOCK GAF Corp said its board has authorized the repurchase from time to time of up to seven mln of its common shares, or about 21 pct, for cash in open market purchases or private transactions. The company said it repurchased 2,100,000 shares under an April authorization to buy back up to three mln shares and authorization for further repurchases under the old program has been withdrawn. Yesterday, GAF said a group led by chairman Samuel J. Heyman has decided to reconsider its offer to acquire GAF. GAF said a revised offer by the group is still possible.