The Communications Workers of America and American Telephone & Telegraph Co. agreed yesterday on a measure that protects jobs, wages and benefits of nearly 235,000 union-represented workers affected by the proposed breakup of AT&T.

The agreement removes a major threat to continued labor peace in the domestic telecommunications industry, which is facing one of the largest corporate divestitures in history.

The accord, reached after six weeks of talks between top CWA and Bell System officials, amends and broadens a job-protection provision contained in the union's 1980 contract, which expires next year.

Under a "successorship memorandum of agreement," the 1980 pact guarantees jobs, wages, benefits and union rights of all employes transferred to new divisions or affiliates within AT&T. But CWA President Glenn Watts and other union leaders argued that it included no protection for employes of companies shorn from AT&T.

AT&T promised the Justice Department Jan. 8 that it would divest itself of 22 local telephone companies with combined assets of about $80 billion. Last month, the company proposed to restructure the 22 companies into seven regional corporations. This would affect about 235,000 of the estimated 525,000 CWA members in the Bell System.

Under terms of the agreement reached yesterday, affected workers are:

Protected against loss of employment, current salary, seniority and changes in the condition of their employment for seven years from the time they are transferred to a divested unit.

Guaranteed the right to receive whichever financial transfer benefit is greater, the former employer's or the new one's.

Protected against reductions in pension, disability and insurance benefits for seven years from the time of transfer.

The amended job-protection agreement takes effect immediately and remains in force until 1987. After that, it can be renewed automatically, unless one or both parties decide to change or end the agreement.

"We have overcome one of the most serious problems we faced because of divestiture," Watts said in announcing the amended job-protection plan. "Now that we know employe interests will be protected, we can go on to other matters."

AT&T spokesman Pick Wagner said that the company "is pleased with the agreement" and that the measure "demonstrates the company's continued concern and interest in its employes."

CWA has indicated that it will join AT&T's announced lobbying effort to defeat legislation that would alter key elements of the Bell settlement. AT&T has called the legislation, approved Thursday by the House telecommunications subcommittee, a "bad bill."

However, the other major union of Bell employes, the International Brotherhood of Electrical Workers, said yesterday that it would not support AT&T's lobbying.

IBEW is negotiating a job-security agreement. In a letter to locals yesterday, IBEW President Charles Pillard said such an agreement will not "answer all of our concerns . . . we still have a real interest in the legislation . . . we ask that you do what you can to withstand the pressure to jump on the bandwagon" to oppose the bill.

IBEW represents about 100,000 Bell System workers. AT&T has more than one million employes.