THE WINTER boat shows offer added benefits to prospective boat buyers this season. After nearly two years of rock-bottom sales, it's anticipated that dealers will be offering show attendees bargain prices, lots of package deals and easy financing. This likely is a reflection of nearly two years of lower than normal boat sales by marine dealers throughout the nation.

To prepare the prospective boat buyer, the National Marine Manufacturers Association offers a step-by-step "Guide to Affordable Boat Buying." It includes information on financing, maintenance, current average price ranges and monthly ownership costs for nine of today's most popular boating rigs. For a free copy write to: NMMA C'mon Aboard, 401 N. Michigan Ave, #1150, Chicago, IL 60611.

Below is a partial list of the boat and outdoor shows in the mid-Atlantic region this winter. Shortly after the show season ends, it will once again be time to go fishing. See you at the shows. CHESAPEAKE SPORTFISHING SHOW -- National Guard Armory, Annapolis, Friday through Sunday. 301/841-6974. NEW YORK NATIONAL -- Jacob Javits Center, New York, Friday through Jan. 13. 212/684-6622.BASS EXPO '91 -- Maryland State Fairgounds, Timonium, Md., Jan. 11 to 13. 301/574-6139. WASHINGTON BOAT SHOW -- Washington Convention Center, Washington, Jan. 16 to 21. 703/569-7141. PHILADELPHIA BOAT SHOW -- Philadelphia Civic Center, Philadelphia, Jan. 19 to 27. 212/684-6622. DELAWARE SPORTFISHING SHOW -- Nur Temple, New Castle, Del., Jan. 25 to 27. 301/841-6974. CHESAPEAKE BAY BOAT SHOW -- Baltimore Convention Center, Baltimore, Jan. 26 to Feb. 3. 301/385-1800. MID-ATLANTIC BOAT SHOW -- The Pavilion, Virginia Beach, Va., Feb. 9 to 17. 804/491-5160. MARYLAND OUTDOOR EXPO -- National Guard Armory, Pikesville, Md., Feb. 15 to 17. 301/841-6974. SEASIDE BOAT SHOW -- Ocean City Convention Center, Ocean City, Md., Feb. 15 to 17. 301/632-2582 or 301/524-9000. SALTWATER SPORTSMAN'S NATIONAL SEMINAR SERIES -- Maryland Hall for the Creative Arts, Annapolis, Feb. 22 to 24. 305/769-0325. A.S.M.A. SPORTFISHING EXPO 91 -- Civic Center, Salisbury, Md., March 1 to 3. 302/629-2118. ACCA SPORTFISHING EXPO 91 -- Virginia Beach Dome, Virginia Beach, Va., March 22 to 24. 804/430-1903. CHESAPEAKE SPORTFISHING 91 SEMINAR -- Holiday Inn, Solomons, Md., April 6 to 7. 301/798-0601.