American Telephone & Telegraph Co. will offer its experimental videotex service commercially for the first time late next year, enabling customers in the Miami area to receive shopping, educational and entertainment information on home computer terminals, company officials said today.

The videotex service has been undergoing a two-year test by AT&T and its partner, Knight-Ridder Newspapers, involving several hundred customers in Coral Gables. AT&T is conducting a second videotex trial in New Jersey with CBS. Customers have had free, two-way access to the service, enabling them to select the information they want, and to pay some of their bills electronically, as well.

AT&T will provide the equipment for the commercial venture in Miami, with the information coming from Knight-Ridder. No charges or fees have been set yet, nor have other cities been selected, AT&T officials said.

The terminals will be provided by American Bell Inc., the new, separate subsidiary that AT&T is establishing to sell telecommunications equipment under a Federal Communications Commission decision deregulating communications services. AT&T today named the officials who will run American Bell when it begins operations Jan. 3.

"We have great expectations" about the videotex services, said Randall Tobias, who will be president of American Bell's Consumer Products division. Tobias had been AT&T's vice president for residential marketing. "We have learned a great deal from the trials, and we know these are services the public wants," he added.

Meanwhile, AT&T also named AT&T Executive Vice President Charles Marshall president and chief executive of American Bell and named Archie McGill, the company's vice president for business marketing, as president of American Bell's Advanced Information Systems division.

At a press conference, the three American Bell executives, along with AT&T Vice Chairman James Olson, outlined the general plans for American Bell, which will employ about 28,000 people in 48 states.

They had little to unveil about specific marketing and product strategies, however. The only major new American Bell venture announced so far is a data communications network known as Net 1,000.

McGill said the service has signed up "five to seven" major customers, but noted that its market development has been hampered by the service's limited capacity.

Within two weeks, AT&T officials hope to file with the U.S. District Court the massive plan outlining details of the corporate divestiture scheduled for Jan. 1, 1984, under the Bell System's landmark agreement with the Justice Department.