The Justice Department yesterday ordered the seven regional Bell telephone companies to immediately stop promoting their credit cards used for charging long distance telephone calls and said it is investigating whether the companies violated the Bell System breakup agreement by issuing the cards.

That agreement spun the companies from American Telephone & Telegraph Co. on Jan. 1, 1984, and prohibits the regional companies from offering long distance service and from giving more favorable treatment to any long distance company.

Acting Assistant Attorney General Charles F. Rule said in letters to Bell Atlantic Corp. and the other regional telephone companies that their use of long distance calling cards "discriminates in favor of AT&T" because all long distance calls made with the card are placed through the regional companies' systems and AT&T. Similar arrangements are not possible with other long distance companies, such as MCI Communications Corp.

This information is not disclosed in advertising examined by the department so far, Rule said. The calling cards "may mislead consumers" because they can easily assume the long distance calls they make will be carried by a long distance company other than AT&T, he said.

Long distance calls made using regional Bell calling cards are automatically routed to AT&T through a computer system set up before the breakup. Because of technical limitations, long distance calls completed using the Bell Atlantic card, for example, will be carried by AT&T even if the customer subscribes to a different company's long distance service.

Justice had expected the system to be changed so that calls could be billed to alternative long distance companies. But such a calling card is unlikely to be issued by the companies before 1989.

Bell Atlantic said yesterday it "takes issue" with the Justice Department. "We don't feel we've violated the {Bell System breakup agreement} in any way and will provide our response to the DOJ within the 20-day period." Bell Atlantic has just started distributing a new regional calling card to more than four million business and residential customers of its local telephone companies in the District, Maryland, Virginia, West Virginia, Delaware, Pennsylvania and New Jersey.

The Justice Department ordered Bell Atlantic to immediately terminate any advertising or promotion of the cards for long distance calling. Bell Atlantic was also ordered to replace any Bell Atlantic calling cards bearing an AT&T international calling number in addition to a regular billing number. The international calling number, which would give preferential treatment to AT&T, is to be deleted on the replacement cards.

Also, the companies must notify customers that other companies issue cards for long distance calling and that they can contact the companies for more information. Although the cards can be used throughout the country, Justice ordered the companies to notify customers that their cards are intended solely for the purpose of making toll calls within a customer's immediate calling area.

The agency has requested information from the companies on their charge card systems and asked for information about possible alternatives. A combination of complaints by companies such as MCI and consumer groups led to the investigation.

Justice Department lawyers also became interested when when they received unsolicited Bell Atlantic calling cards in the mail, sources said.

"What they were doing was outrageous," said John Worthington, general counsel for MCI. "They were defaulting all calls to AT&T without telling the customers and making it look like they were the long distance carriers when they are not allowed to be."