The breakup of American Telephone & Telegraph Co. doesn't have to result in higher rates for consumers, but it will be more troublesome for them, a consumer forum was told here yesterday.

"You will have to do more work," said Bob Nichols of the Consumers Union. "You won't be able to make one call to get service connected, to have a dial tone and to connect to anywhere in the world."

Those consumer headaches stem from the fundamental changes coming about as a result of the government-ordered breakup of AT&T. Under the reorganization, which began this year and continues through 1984, consumers gradually will be faced with going one place to buy equipment, to another place to arrange for hookup and to another for long distance service.

Nichols, speaking at a workshop at the annual Consumer Assembly, said that consumers are wrong to complain about the new environment and to call for a return to the "1950s when one telephone company was in control" of communications.

Moreover, complaints could have a harmful effect, leaving regulators with the impression that consumers are children, Nichols said. "My call is for consumers to participate meaningfully [in divestiture] . . . We need to have more serious hard evidence of feelings we have about phone service" when taking positions on telephone issues, he said.

Nichols urged consumers to concentrate on documenting the serious issues of divestiture and "force regulators to really look at costs" to determine if there is justification for rate increases.

"It may be true that divestiture will mean higher rates--but we don't know that," he said. "And by taking the position that rates will increase, we can be sure that they will go up."

Harry Trebbing, director of the Public Utilities Institute at Michigan State University, also urged consumers to approach their task seriously.

Trebbing outlined some specific steps that consumers should take in responding to telephone divestiture: examine prices for service and equipment to determine the impact on competing companies; seek at least some open trading of the stock of American Bell, the new equipment sales company spun off from AT&T; fight to have state regulators get back their authority over telephone company depreciation methods; and pressure regulators to unbundle rates so that consumers can buy the equipment on their premises at the net book value. Finally, consumers should search for methods for capping prices for small-volume telephone users.

The Consumer Assembly is sponsored by the Consumer Federation of America, which claims to represent 200 groups and 30 million consumers.