Unemployment dipped to 5.3 percent in December, the government said Friday, as the economy created 280,000 jobs with the strongest gains in service industries. In falling 0.1 percentage point to 5.3 percent, the nation's civilian unemployment rate matched a low point for the year set in October and was the strongest rate in 14 years, according to the Labor Department's Bureau of Labor Statistics. During 1988, employment increased by 2.3 million with adult women accounting for about two-thirds of the gain and adult men about one-third of the improvement. (See Utah jobless report on A3.)