Ma Bell's fledglings will be big - and unpredictable

The chief executives of American Telephone & Telegraph's soon-to-be-spun-off parts have been jetting to Chicago, New York, San Francisco - all the major cities - to talk up their companies to stockbrokers. They are showing company movies and slides, pointing to a bright future ahead.

But even now, after all the presentations and just four months away from the breakup of the world's biggest company, it's just ''too difficult to predict'' the financial future of these new independent phone companies, says James McCabe , an analyst following AT&T for Prudential-Bache Securities.

When divestiture happens on Jan. 1, the 22 local Bell operating companies will be detached from AT&T and regrouped into seven regions, each group owned by a new regional holding company.

With rate increases still an unknown, expected revenues are unknown. ''I have no data to go on,'' Mr. McCabe exclaims. Congress is likely to pass legislation this fall that would change the rate picture anyway. And the companies won't be giving out dividend information until November.

Finances may look fuzzy, but the structure and strategies of the new holding companies are coming into focus. One thing is sure, they will look fairly similar at the outset. No matter what you hear about the new, exciting businesses these companies are tackling, ''in their first several years they will clearly be telephone companies,'' McCabe says. ''And there will not be a whole lot of difference between them.''

The regionals will be no small potatoes. Their assets will be roughly the same, ranging from $14 billion to $21 billion. In terms of assets, they will rank among the top 15 US corporations. They will outsize any of the country's electric utilities. Their customer bases will also be roughly the same, and they will have a similar number of employees, 80,000 to 100,000.

What will differentiate these telecommunications giants will be the economies of their regions, their geographic location, their modernization, their management, and the new businesses they enter (see story on Page 12).

Basically, the holding companies can enter whatever businesses they want, though they have to have permission from the US District Court in Washington, D.C., on each one - ''a significant regulatory barrier,'' one analyst comments. (For instance, some of the companies would like to establish data bases - large information banks that customers would subscribe to and reach by phone. But they can't until they prove that they are not creating a monopoly situation.) Also, the companies can't make phone equipment, but they can sell it. And the long-distance business is off limits, too.

One business all the regionals are getting into is cellular phone service. This involves a technology that allows many more mobile phones to be used in an area than before.

''I don't think anyone would dare not do cellular in their territory,'' says Andrew Silton, an analyst with First Albany Corporation. ''They would be giving it away to non-phone companies'' that are competing for the business too, Silton says. The business is ''fairly capital intensive and will not earn them any money in the near term.'' Zane Barnes, designated chairman of Southwestern Bell Corporation, isn't expecting profits from the cellular business for five years yet.

But the business has tremendous potential. ''I see cellular going from a phone in the car, to a phone in the briefcase, to a phone in the pocket,'' comments William Weiss, the designated chairman of Ameritech, the Midwest holding company. Analysts estimate cellular will be pulling in $2.7 billion in revenues annually, nationwide, by the end of the decade.

The holding companies are gearing up for another business - customer premises equipment. They don't like the idea of selling phone equipment to residents, but business customers are another story. ''The residential market is a commodity business. You can go into any store today'' and buy a phone, Ameritech's Weiss points out. Businesses will need switching systems, sophisticated phones, and lines - and the regionals are eager to start selling. But analysts point out that this business will also be highly competitive.

Competition - that's a sore spot with these companies. They complain about issues like bypass, whereby a company sets up its own cable or microwave tower to connect long-distance calls directly with a long-distance carrier, like MCI or Sprint. This way, it avoids the costs of going through the phone company to make the connection.

The regionals say they can't compete effectively for business customers because they can't price their services competitively. Because of divestiture, they are losing the long-distance revenue that has always subsidized the high cost of local calls. Yet local rates are still being regulated at below cost. The holding companies would like to see regulators move toward measured service, under which phone rates would be based on the cost of providing that service.

When the Federal Communications Commission approved an access fee plan in July, it was a step in this direction. The plan is designed eventually to replace the long-distance subsidy with revenues from local consumers. This shift will start next year by adding $2 a month to the cost of a residential phone line, and $6 a month to the cost of a business line. What the customers will be paying for is access, through their local phone company, to a long-distance carrier.

With Congress uncertain as to what it will do about phone service legislation , and with major local rate cases pending, executives and analysts agree that regulation is now the major concern for these phone companies.

''The key trouble,'' comments Andrew Silton, the First Albany analyst, ''is going to be regulatory.'' He thinks that in the end, ''those utility commissions really don't have any choices. They are going to have to do it (raise rates and restructure them).''

But Congress and the public are likely to put up a loud cry. And in the ensuing months ''you'll see a lot of fireworks,'' another analyst comments.