A group of meatpacking industry executives made profits averaging $2.5 million apiece in less than 18 months by speculating in the cattle futures market, a congressional study of insider trading in the beef business disclosed yesterday.

The 22 meat industry insiders pocketed more than $56 million and were the biggest winners in the beef futures market during the period studied by the House Small Business Committee.

The multi-million-dollar insider dealings disclosed by the study "suggested that individuals privy to insider trading information be prohibited from buying or selling futures contracts," said Rep. Neal Smith (D-Iowa), chairman of the committee and a long-time critic of the cattle futures market.

Officers of publicly owned corporations are prohibited from using inside information for personal investments in the stock markert, but there are no legal restrictions on insider trading in commodities.

Smith's committee did not name the meat industry executives who made a windfall profits but they said they were officers of meatpacking companies, meat processors, grain and feedlot companies.

The study showed the second-most-successful group of traders in the Chicago Merchantile Exchange's cattle futures market were officers of commodity brokerage firms, who made profits averaging $804,000 each over a 16-month period. Commodity brokers also are exempt from the kind of insider trading regulations that apply to stockholders.

The insider profits in the cattle futures market were discovered when the Small Business Committee staff analyzed confidential reports filed with the Commodity Futures Trading Commission by major traders between January 1978 and April 1979.

Anyone who owns more than 50 futures contracts must report the holdings to the CFTC, the federal agency that oversees the markets. About 1,000 commodity traders had big enough holdings in cattle futures to file reports during the period covered.

Cattle futures are contracts for future delivery of beef cattle. Each contract is for 40,000 pounds of beef on the hoof. Few cows ever change hands in the cattle futures business. Most transactions are settled by paying in cash the difference between the price of cattle when the contract was "signed" and when it comes due.

The small business panel study found that during the 16 months farmers never owned more than 7 percent of the cattle contracts. During that time small investors -- those with fewer than 50 contracts -- lost $155 million in the market. The most active traders -- and the most successful -- were the meat industry executives. Big traders as a group made about $155 million in profits.

Smith said the study shows the CFTC needs to limit the holdings of big speculators and close loopholes in Chicago Merchantile Exchange rules that give advantages to insiders.