Getting a head start on divestiture, Chesapeake & Potomac Telephone Co. will begin sending out new-style telephone bills next week to reflect the impending change in the company's ownership when it is spun off from the American Telephone & Telegraph Co. on Jan. 1, 1984.

The new bills will be bulkier and more detailed than current bills, breaking down components of telephone service that are now lumped in one category into several separate charges.

The average three-page bill will become an eight page document under the new system, C&P officials say.

Customers will receive separate invoices for local phone service and equipment, which are currently grouped together. Similarly, there will be separate page listings of long-distance calls made outside the local area and long-distance calls made within C&P's local service area. Currently these calls are all billed under one long-distance phone invoice.

The change in telephone bills will be the first evidence many customers see of the breakup of AT&T. The separate bills reflect the fact that after Jan. 1, AT&T's long-distance network will be a separate company not affiliated with C&P's local phone service.

Other changes in phone service will follow the new bills. However, it will be at least another year before consumers begin seeing one of the chief benefits of divestiture--easier access to AT&T's long-distance competitors.

Until at least September 1984, consumers who want to make long-distance calls through MCI, Sprint or other long-distance networks will still have to dial 12 extra digits before they can make their calls.

And it may take until September 1986 before all customers will be able to hook into one of AT&T's long-distance competitors by dialing a single number, as they do now when they call over AT&T's lines.

C&P executives say they are trying to make the transition to the post-divestiture world as smooth as possible by issuing the new bills three months ahead of the scheduled breakup.

After divestiture, C&P will have to include in its billing a disclaimer telling customers "there is no connection between C&P and AT&T. You may choose another company for long-distance calls (or equipment) while still receiving your local service from C&P."

No such disclaimer will appear in the new bills going out next week. "We do not plan to put in that disclaimer until Jan. 1 since we are still owned by AT&T," said C&P spokesman Web Chamberlin.

Although the new bills may be confusing to C&P customers, company officials say that, ultimately, bills will be less complex than they are now. "Consumers will now know clearly which charges are which, with equipment and local service being separated instead of grouped together," said Chamberlin.

C&P and several other local operating companies of the Bell System are revising their bills three months ahead of the scheduled breakup as part of an overall Bell System plan of simulating the post-divestiture world as soon as possible.

After divestiture, AT&T's 22 local operating companies will be spun off from the Bell System, with each operating company becoming part of one of seven newly created regional telephone companies.

Though long-distance service will remain with AT&T, C&P will handle the billing for AT&T--and any other long-distance carrier that wants it--for a fee. Equipment owned by C&P, including telephones consumers now have in their homes, will belong to AT&T, unless customers chose to buy it outright. If consumers continue to lease their phones, C&P will handle the monthly billing fees for AT&T.

When C&P is no longer owned by C&P, it will have to update its technology to permit its customers to use AT&T's long-distance competitors as easily as they now use AT&T. Now, a customer wanting to use a competitor must first dial a seven-digit local number and then a five-digit identification code to hook into the long-distance network.

But after divestiture, C&P will update its switching equipment so that a customer will be able to chose which long-distance carrier he or she prefers to use and access it easily.