The stock market suffered one of its broadest setbacks of the new year today in a selloff blamed on cold-weather and energy worries.

The Dow Jones industrial average, made up of 30 blue chip stocks, fell 8.40 to 933.84, and extended its loss so far in 1977 to more than 70 points.

What caught many analysts' attention, however, was another statistic - the 5-2 margin by which losers outnumbered gainers on the New York Stock Exchange.

That signalled selling pressure on a number of the secondary stocks that had held up well in the past several weeks while the blue chips and glamors represented by the Dow had been falling steadily.

At the American Exchange, home of many smaller stocks, the market value index fell .81 to 112.43, breaking a string to six straight gains.

Big Board volume reached 23.64 million shares, against 24.04 million on Tuesday.

Nationwide turnover in NYSE listed issues, including trades in those stocks on regional exchanges and in the over-the-counter market, came to 27.65 million shares.

General Motors, often regarded as a bellwether issue because of its standing as the country' largest manufacturing corporation, fell 2 to 71 as of the 4 p.m. close at the NYSE. The stock led the active list on turnover of better than 535,000 shares.

Among other auto industry stocks, Ford Motor dropped 1 3/4 to 56 1/4 and Chrysler was down 1/2 at 20 1/4.

The NYSE's composite index dropped .47 to 54.86.