The Supreme Court yesterday refused for the second time this year to grant a request by American Telephone & Telegraph Co. to intervene in the government's effort to break up the Bell System.

The Justice Department, in a civil antitrust suit filed three years ago, accused AT&T of attempting and conspiring to monopolize, and with monopolizing, telecommunications services and equipment. The government's proposed remedies include divestiture of Western Electric, Bell's manufacturing subsidiary.

Bell claims it enjoys implied immunity from antitrust liability because it is subject to regulation by the Federal Communications Commission and the states.

After a federal judge here rejected the claim, AT&T asked the Supreme Court to review his ruling even before it was acted on by the U.S. Court of Appeals for the District of Columbia. The Supreme Court refused to do so on May 26.

Yesterday, the court refused a Bell petition to review the appellate court's ruling. The government had told the court that "piecemeal review by extraordinary writ is inappropriate."

Bell chairman John DeButts said AT&T is "disappointed" and renewed warnings that the suit "could become the most complex and expensive antitrust litigation in the nation's history."