But mass advertisers are trying the medium too. Bristol-Myers and Anheuser-Busch have signed multimillion-dollar, multiyear contracts with cable networks that supply programming to local cable operators via satellite.

As a result of its contact, Busch's six beer brands will be the only ones advertised on the Entertainment and Sports Programming Network, which supplies 24 hours a day of sports to an audience that Michael Trager, executive vice president of D'Arcy-MacManus & Masius, the Busch agency, says, ''fits the profile of the kind of guy we want.''

That profile is the better-than-average-educated male with a better-than-average income, which is the kind of person who makes up a large component of the cable television audience.

''If, long-term, you accept a concept that cable will become an important medium for advertising, the sooner you get in and get experience the better it is for your company,'' Marvin H. Koslow, vice president for marketing of Bristol-Myers, said.

Bristol-Myers, a large pharmaceuticals and household products company, is also experimenting on the local cable level in San Diego. That is the home of KCOX Channel 2, a multiple-system cable operator that uses the call letters, which are not official, in order to better compete in a broadcast-oriented market. William Gruber, its general manager, said he has dealings with some of the country's largest advetising agencies since KCOX - with 300,000 subscribers, or 47 percent of the market local market - is the country's largest multiple-system operator.

Industry analysts say a relationship will have to develop between multiple system operators and national advertising representatives if cable is to become a national advertising carrier. It is expected that ultimately there will be 7,000 systems in the country, and national advertisers and their agencies could not begin to deal with them as individual buys.

''Multiple system operators are now vying for major market franchises and they are more sophisticated than the mom and pop operators who are not advertising oriented,'' Ira Tumpowsky, vice president and newly appointed head of cable in the media department of Young & Rubicam, said.