Pettay, who was appointed to FIFA's international referees list last year, was among 44 people killed when a RusAir passenger jet flying from Moscow to Petrozavodsk crashed in heavy fog. He was 37.
Blatter writes to Russian Football Union leader Sergey Fursenko that the football community stands by Pettay's family, friends and loved ones.
Fursenko says the RFU will help support Pettay's wife and two children.
Pettay had refereed European Championship qualifying matches at under-21 and under-17 level, and was an additional assistant in Champions League games last season.