Civil Aeronautics Board Chairman Dan McKinnon warned commercial airlines yesterday that they risk loss of their licenses and U.S. landing rights if they fail to control drug smuggling on their aircraft or by their employes.

The CAB is "not going to sit idly by," he told an Aero Club luncheon here, but will crack down on the airlines unless they do what is necessary to "guarantee they do not become conduits for the drug trade."

He named no airline, and cited only one incident in which a commercial airliner was used for large-scale drug smuggling. In March, a customs inspector at Miami International Airport discovered 3,748 pounds of cocaine in a container labeled "clothing" that had just arrived on a flight from Colombia.

Though McKinnon used strong language, officials in both law enforcement and the airline industry were skeptical about the practical impact of any action the CAB might take.

A spokesman for the Drug Enforcement Administration said drug smuggling on commercial airliners is "not that big a problem" compared with the use of private planes and boats.

Airline industry officials noted that it is the responsibility of the customs service, not the CAB, to watch for illegal drugs. They said the CAB -- which is scheduled to go out of existence because of airline deregulation at the end of 1984 -- lacks the means to check on the activities of baggage-handlers or airliner cabin crews.