Gregory Oskoian, 51, secretary-treasurer of the newly merged Bakery, Confectionery and Tobacco Workers International Union, died of a heart attack Monday in Winchester, Va. He had been on a vacation there. He was a resident of Washington.

He came to this area after his election in December 1969 to the position of executive vice president of the Bakery and Confectionery Workers International Union of America. He became secretary-treasurer of that union in 1970.

The union and the Tobacco Workers International Union merged last month at a Las Vegas convention, and Mr. Oskoian was elected then to a new term as secretary-treasurer. He had played a key role in bringing about the merger.

Mr. Oskoian was born in Providence, R.I. He played with the Navy Band in 1945-46. He started work at an AP bakery in Cranston, R.I. in 1950, and joined the bakers' union.

Starting in 1957, when he was elected business agent of his local union, he moved up through the ranks to international representative, international vice president and then executive vice president.

He is survived by his wife, Julie, and a daughter, Cheryl Ann Daly, both of Potomac; two sons, Greogory J., of Gaithersburg, and Gary J., of Germantown, Md.; his parents, Mr. and Mrs. Oscar Oskoian, two sisters, Barbara Muksian and Margaret Pelegian, and a brother, Jack, all of Cranston: another brother, George, of Monroe, La., and two grandchildren.

The family suggests that expressions of sympathy may be in the form of contributions to the building fund of St. Mary's Armenian Apostolic Church in Washington.