William Trenk;76;of (Fairhope);Belle Vernon;died Friday;May 17;1996;in the Monongahela Valley Hospital after a short illness.  He was born May 5;1920;in Fairhope;the son of the late Louis and Anna Tomaja Trenk.  Mr.Trenk was Catholic by faith and a member of the Holy Spirit Roman Catholic Church of Fayette City.  He was also a retired employee of the Washington Township Municipal Authority.  He was a veteran of World War II;having served with the U.S.Army;where he received a Purple Heart for his wounds.   He also was a member of the Brightwell Daugherty Post 484;American Legion of Fayette City;V.F.W. Post of Belle Vernon and the Fairhope Rod and Gun Club.  Survivors include his wife of 50 years;Helen (Melanowsky) Trenk;two daughters ans sons-in-law;Linda and Raymond Rathway of Perryopolis and Michelle and William Moody of Fayette City;one son;William Trenk of West Newton;nine grandchildren;Mrs.Robinette (Rathway) Vitez;Mrs.Ronna (Rathway) Sabol;Raelynn Rathway;Douglas;Charles and Rosemary Trenk and Scott;Shawn and Christopher Moody;one great-grandson;Brandon Sabol;three sisters;Betty Badock and Ann Belsick;both of Belle Vernon;and Marge Galilei of Monessen.  In addition to his parents;he was preceded in death by two brothers;Louis and Joseph Trenk.  Friends will be received Saturday from 2 to 4 and 7 to 9 p.m.and Sunday from noon to 4 and 7 to 9 p.m. in the Howard W.McCrory Funeral Home;334 Main St.;Fayette City.  A parish wake service will be held Saturday at 8 p.m.  A Prayer service will be held Monday at 9:30 a.m.in the funeral home;followed be a Funeral Mass at 10 a.m. in the Holy Spirit Roman Catholic Church of Fayette City with the Rev.Richard E.Mackiewicz as celebrant.  Interment will follow in the Belle Vernon Cemetery.  The Howard W.McCrory Funeral Home is in charge of arrangements.