WPCNR WHITE PLAINS AFTER DARK. July 11, 2004: George Gretsas, the outgoing Mayor's Executive Officer, will be given a sendoff by his many friends, admirers, colleagues, commissioners, developers and county cronies Thursday evening at Laguna Restaurant from 5:30 to 8 P.M. The indefatigable Executive Officer who has been working virtually around-the-clock for six-and-one-half years to create the White Plains Renaissance will apparently break away from his corner office and cellphone for a goodbye party. The party, the Mayor's Office says is not by invitation only, but "anyone who wants to can come." The cost is $35 a head. R.S.V.P. to the Mayor's Office at 4221411