Europe has retained Golf's Ryder Cup, easily defeating the United States for its eighth victory in the last 10 times in the biennial event. The 12 man European team, a collection of the continent's best professional golfers, held a commanding four point lead heading into yesterday's decisive singles matches at the Gleneagles course in Scotland, and added to its margin, finishing ahead 16 1/2 to 11 1/2. The Europeans won five matches yesterday, the US four, and three ended in ties.