International Telephone & Telegraph Corp. filed a $150 million federal suit today against American telephone & Telegraph Co., charging its competitor with antitrust violations involving equipment purchases.

IT&T said AT&T and its subsidiary firms of Western Electric Co. and Bell Laboratories Inc. violated the Sherman and Clayton antitrust acts.

The suit charged that AT&T deliberately refused to purchase telephone equipment made by firms other than its own subsidiaries, even when the outside equipment was technically superior and cheaper. The suit was filed in federal court here.

AT&T, the nation's largest utility, said it had not seen a copy of the suit and could not comment.

ITT said that since 1970 it had lost profits of at least $50 million on its telephone transmission equipment. The company is suing for triple damages, as authorized under the antitrust laws.

ITT alleged in court papers that Western Electric sold more than $230 million of its own channel bank equipment to Bell companies in 1973-74, while ITT was only able to sell $5 million of its less expensive equipment to Bell that year.

IT&T said AT&T's telephone service branch, Bell Telephone, purchases the vast bulk of its equipment from Western Electric, Technical evaluations of outside equipment are performed by Bell Laboratories, which is jointly owned by AT&T and Western Electric. Western Electric's sales to Bell companies exceeded $6 billion in 1976.

Bell Telephone companies provide about 80 per cent of the nation's telephone service.

The suit charged that the defendants engaged in an unlawful combination to monopolize interstate trade and commerce in telecommunications equipment, preventing IT&T and other outside suppliers from entering the market.

The case was assigned to U.S. District Judge Gerald L. Goettel.

In 1976, AT&T had gross revenues of $325 billion and net income of $3.8 billion.

IT&T, which makes telecommunications equipment in about 80 countries, also has such diverse operations as food processing, auto parts manufacturing and insurance. Its revenues last year totaled $11.8 billion and its income $488.7 million.