Stock prices fell in light trading today, starting off the final quarter of 1988 on a wary note. The Dow Jones average of 30 industrials, down 6.40 on Friday, dropped 21.52 to 2,091.29 by 2 p.m. today on Wall Street. Losers outnumbered gainers by 3 to 1 in nationwide trading of New York Stock Exchange-listed issues, with 359 up, 1,079 down and 414 unchanged. Wall Streeters were generally resigning themselves to a sluggish week, expecting investors to back away from stocks before the government issues its monthly report Friday on the employment situation. Analysts look for the data to show a pickup in payroll employment growth for September after relatively modest increases in July and August. If those estimates prove correct, it would come as a setback to hopes that the economy was slowing to a pace that would satisfy the Federal Reserve, which is seeking to keep inflation from heating up. The Commerce Department reported today that new factory orders rose 3.1 percent in August. Losers among the blue chips included Exxon, down | at 44[; International Business Machines, down 1 at 114]; American Telephone & Telegraph, down \ at 25}, and Coca-Cola, down 1[ at 42|. Technology issues were notably weak. Digital Equipment fell 1{ to 92], and Hewlett-Packard 1 to 48~, while in the over-the-counter market Intel lost 1} to 25} and Apple Computer was down 1\ at 42. Middle South Utilities bucked the downtrend, rising [ to 15[ in active trading. On Friday the company declared its first common-stock dividend in three years. The NYSE's composite index of all its listed common stocks dropped 1.22 to 152.35. At the American Stock Exchange, the market value index was down 1.97 at 299.66. Volume on the Big Board came to 88.55 million shares with two hours to go.