EDMONTON, Alberta, Jan. 27 (AP) — Wayne Gretzky of the Edmonton Oilers celebrated his 13th birthday yesterday by signing an agreement to extend his current seven‐year World Hockey Association contract to 21 years.

Edmonton's Wayne Gretzky signing 21‐year contract as Larry Gordon, term's vice president, looks on

The agreement will keep the star teen‐aged center an Oilers’ employee until 1999.

Terms and conditions of the deal were not disclosed although it was reported to be worth $5 million. Gretzky's seven‐year contract was signed for a reported $1.75 million.

The contract was signed at cen- ter ice before the Oilers met the Cincinnati Stingers and was witnessed by Gretzky's mother, father and three younger brothers.