The nation's largest group of corporate communications users opposes pending legislation that would deregulate key facets of the telephone industry, claiming the plan is unlikely to make the industry more competitive.

The International Communications Association, a trade group that represents large companies and other institutions that spend about $10 billion a year for telecommunications, made the announcement last week at the close of the organization's annual conference here.

The policy statement is said to reflect concern about the legislation and increasing distrust of the potential primary beneficiary of the legislation, American Telephone & Telegraph Co. AT&T would be permitted to offer an array of new services, including sophisticated data-processing services, if the bill -- now before a Senate committee -- becomes law.

But many conference participants, companies with historic ties to AT&T, expressed deep concern about major long-distance rate hikes recently announced by the telephone company.

"Existing carriers like AT&T have a market power that overwhelms most segments of the marketplace," said Robert Bennis, manager for communications systems at Westinghouse Electric Corp. and the chairman of the association's regulatory committee.

"The legislation currently before the Senate clearly does not contain the proper formulas to create conditions which would foster the development of full and fair competition," the group said in a policy statement.

The association said the assumption that competition is "widespread" in the industry -- a point the group said appears implicit in the bill -- is "totally incorrect" and noted many suppliers of equipment and communications services "follow the price leadership" of large carriers such as AT&T.

Announcement of the opposition to the legislation from the potentially powerful group of very large companies -- many of whom are among the largest 500 industrial business in the country -- came as the Senate Judiciary Committee announced plans to conduct hearings on the antitrust situation in the communications industry.

A spokesman for Sen. Strom Thurmond (R-S.C.), chairman of the Judiciary Committee, said the committee would hold a hearing Wednesday on "monopolization of the telecommunications industry." Although no witness list has been completed, Assistant Attorney General William Baxter may be asked to testify.

The hearing is particularly important because Thurmond has asked for a referral of telecommunications legislation, if it passes the Commerce Committee, to review it in light of antitrust concerns.

Baxter, chief of the Justice Department's Antitrust Division, has written to the Office of Management and Budget to complain that the legislation, introduced by a coalition of Senate Republicans, including Sen. Robert Packwood (R-Ore.), chairman of the Commerce Committee, would jeopardize the department's ability to break up AT&T in the government's massive antitrust suit against the Bell System.