U.S. District Judge Harold H. Greene, who presided over the Bell System breakup, yesterday granted 13 waivers to permit six of the seven regional telephone companies enter new lines of business.

The former Bell telephone companies, spun off American Telephone & Telegraph Co. as part of the divestiture agreement, must apply to the judge for permission to engage in activities other than their primary business of providing local telephone service.

Greene had said earlier that companies must establish separate subsidiaries for new lines of business, arrange independent financing, agree to Justice Department monitoring of competitive activities and cap new business investment at 10 percent of the regional company's estimated net revenues.

The 13 requests, made by Bell Atlantic Corp., US West, Pacific Telesis, Nynex, Ameritech and Bell South, "will have no negative impact on domestic competitors of the regional holding companies which are entitled to be shielded from competition having its basis in a monopoly enterprise," Greene ruled yesterday. The activities also will benefit U.S. foreign trade, he said.

Five of the waiver requests were to launch foreign business ventures. Ameritech will provide telecommunications consulting and cellular services abroad. Pacific Telesis, Nynex, and US West will engage in foreign consulting services, engineering, sales of telecommunications systems and offer other services.

US West and Pacific Telesis will be permitted to enter the real estate business. US West and its subsidiary NewVector Communications Inc. will provide cellular radio services in the Gulf of Mexico. Nynex, Pacific Telesis and Bell South will enter the office products business. Bell Atlantic Corp. will be permitted to complete acquisition of the Sorbus Service Division of Management Assistance Inc., a national computer maintenance and repair firm, and Tri-Continental Leasing Corp., an equipment lease financing business.