BREWER and PORTLAND - Timothy Winsor Tower, 44, died Aug. 7, 1997, at a Bangor hospital after a valiant, brave and courageous battle with kidney cancer.  He was born in Bangor, July 8, 1953, the beloved son of Paul and Jacqueline (Robbins) Tower.  Tim was a 1971 graduate of Brewer High School and a 1975 graduate of the University of Maine, where he earned a bachelor degree in chemical engineering.  For the last 10 years, he had been employed as sales manager for National Ski & Bike in Freeport.  Tim was an avid skier at Sugarloaf, St. Anton, Austria and Sun Valley, Idaho.  He loved golf, wind surfing, mountain biking and roller blading, and he was also a great gormet cook.  Surviving, in addition to his parents of Brewer, are two sisters, Michelle Clark of Auburn and Anne Van Atta and her husband, Richard of Stuart, FL; three nephews, Andrew and Michael Clark and Quinn Van Atta; aunts and uncles, C. Bernard and Geraldine Robbins of Bangor, Seldon and Marilyn Blethen of Ellsworth, Thomas and Jeanne Hammond of Brewer, John and Mary Jane Wedin of Orrington, Roland and Dorothy Andrews of Holden, Bud and Anne Allen of Boca Raton, FL, and J. Stephen and Marta Robbins of Bangor; a great-aunt, Mrs. Louis Dutch of Brewer; many loving cousins.  He was predeceased by his grandparents, Mr. and Mrs. A. Windsor Tower and Mr. and Mrs. Clyde Robbins.  He will be greatly missed by his "skiing buddies" at Sugarlaof.  Friend may call 2-9 p.m. Friday at Kiley-Birmingham Funeral Home, 69 State St., Brewer. A Mass of Christian Burial will be concelebrated 11 a.m. Saturday at St. Joseph's Catholic Church, Brewer, by the Rev. Joel Cyr, administrator, and the Very Rev. Richard E. Harvey. Burial will be at Woodlawn Cemetery, Brewer.  For those who wish, contributions in his memory may be made to St. Joseph's Parish, 531 No. Main St., Brewer, MW 04412, or to the American Cancer Society, Maine Division, Inc., 52 Federal St., Brunswick, ME 04011.