The Chesapeake & Potomac Telephone Co. introduces "equal access" to about 3,000 customers in the District of Columbia today. Some parts of both Maryland and Virginia also will have the option.

Local Bell companies across the country are doing the same thing, introducing millions of customers to their first taste of true competition in the long-distance business.

Equal access means customers can choose any long-distance competitor of AT&T to provide long-distance service without having to dial a lengthy code to reach that long-distance company first. Customers using MCI or Sprint, for example, will be able to complete calls by dialing 1, the area code and the number.

Equal access will be phased into the city and Maryland and Virginia suburbs over the next two years, and by September 1986 will be available to the majority of C&P's customers.

About 3,000 telephone customers in Southwest Washington will be the first in the city to select one of 10 long-distance companies. The companies that customers have to choose from are AT&T Long Distance Service, SATLECO, Telesaver Universal Service, MCI Telecommunications Corp., ITT, US Tel., SBS Skyline, Western Union LD Services, GTE Sprint Communications, and ALLNET.

Customers still can use other long-distance companies, but will have to dial a lengthy code to use them.

Initially, the option will be available to 14 exchanges in Southwest: 245, 252, 287, 382, 447, 453, 475, 479, 485, 488, 646, 651, 732, and 863.

Exchanges in the Baltimore-Liberty areas that have the equal access option today include: 367, 466, 542, 578, 664, and 950. Exchanges in the Baltimore-Columbia area that also have the option include: 596, 629, 730, 748, 964, 992, 995, 997.

Other areas that have the option starting today are Philadelphia, Wilmington, Del., Clifton, N.J., and seven other cities around the country.

C&P notified its customers 90 days in advance, asking them to choose a primary long-distance company. These customers will be asked to make a choice within the next nine months. The customers should notify the long-distance company, not C&P, a spokesman said. Long-distance companies will bill customers separately unless they have contracted with C&P to do their billing for them.

There will be no charge from C&P for the first selection of a primary long-distance company chosen before March 1, 1985. There will be charge of $5 after that date.