Ma Bell's stepchild in Connecticut

When is a Bell operating company not really a Bell operating company? When American Telephone & Telegraph owns only 24 percent of its stock, that's when. Because Southern New England Telephone Company is not controlled by AT&T, AT&T was not required to divest itself of its interest in SNET. Instead of playing a role in the breakup, SNET has starred in an adventure drama of its own.

''We weren't put through the divestiture meat grinder,'' says Dan Miglio, SNET vice-president of regulatory affairs. ''We weren't forced to give up to AT&T portions of our intrastate phone business, as the other Bell operating companies were.''

Because it's not part of the divestiture, SNET was allowed into the unregulated equipment business Jan. 1, 1983 - a full year before the other Bells.

Moreover, SNET, unlike other members of the Bell family, was not excluded from interstate long-distance telephone service. It was this end of the business which garnered so many headlines for SNET when it announced last August its intention to build LightNet. This is to be a fiber-optic telecommunications network, in partnership with CSX Corporation, whose railway rights of way it is to use.

Publicity has obscured the fact that no customers have signed up and none of LightNet has been built. SNET officials insist, however, that negotiations with a number of important potential customers are under way and commitments could be announced within weeks.

SNET, which serves most of Connecticut, has had a good base on which to build: The state is small and its population is concentrated along the ''golden banana'' of Interstates 91 and 95. And Connecticut is full of communications-intensive offices such as corporate headquarters and insurance companies. Although Mr. Miglio insists SNET could duplicate its activities in another state, he acknowledges it would be ''a lot harder.''