The Commodity Futures Trading Commission announced yesterday that the New York Commodity Exchange agreed to pay a civil penalty of $70,000 to settle a CFTC charge that it failed to enforce its own rules against a floor broker the agency has accused of illegal trading activities.

The CFTC also announced that it filed a 13-count complaint against the broker, Ira W. Kuhlik, and against Lincolnwood Inc., the commodities firm Kuhlik heads.

Dennis Klejna, director of the CFTC's division of enforcement, said the Commodity Exchange had been informed four times during a four-month period that Kuhlik was making questionable trades and did nothing about it.

The Comex, in agreeing to pay the penalty and to "desist" from violations of the law, did so without admitting or denying guilt.

The $70,000 fine is the second-biggest penalty the 10-year-old agency has leveled against a futures exchange, Klejna said. He said the biggest, a $200,000 fine against the New York Mercantile Exchange several years ago, involved a whole pattern of illegal trading activities by a number of brokers.

In this case, the large fine was assessed when only one broker was engaged in allegedly illegal conduct.

In its complaint against Kuhlik and Lincolnwood, the CFTC said there were 26 gold futures trades that violated Comex and federal regulations between Aug. 11, 1981, and Jan. 4, 1982. The agency said Kuhlik's trades involved more than 16,130 gold futures contracts.

The complaint, which could seek a $100,000 fine for every violation, charges Kuhlik and his firm with illegal cross-trading (matching buy and sell orders privately without exposing them to "open outcry" in the trading pits) and other forms of noncompetitive trading.

The CFTC also alleged in its complaints that Kuhlik and Lincolnwood did business for extended periods without being registered with the commission. The agency also charged that Kuhlik filed false "large trader" reports with the commission.

Last week, the CFTC sued the Kansas City Board of Trade and eight floor brokers, alleging that there was illegal trading in the exchange's stock index contract based on the Value Line stock index. The CFTC also cited Merrill Lynch Futures for failing to properly supervise one of its floor brokers.