Barbara J. Strzepka of Cheektowaga, president of the New York State Federation of World Organization of China Painters, is coordinator of the state federation's 32nd annual convention and exhibit Friday from 9 to 5 p.m. and Saturday from 9 to 4 p.m. in Sheraton Four Points Hotel, Cheektowaga. The show is open to the public and will include demonstrations of painting on porcelain and exhibitor booths featuring artists' supplies. Prizes include a porcelain tea service painted by Linda Alexander of Little Rock, Ark., and a porcelain jardiniere painted by Mrs. Strzepka. A porcelain art auction Thursday at 7:30 p.m. will benefit art education scholarships available to New York State residents who wish to learn the art of china painting. Applications are available from Molly Nemeth, art scholarship chairwoman, 2885 Eggert Road, Tonawanda, N.Y. 14150.