Phone calls by congressional staffers are being put on ''hold.'' As a result of budget cuts for Senate and House committees, staff members have been told not to make any long distance telephone calls unless it is absolutely -necessary, or an emergency. Thus, when a reporter in Boston phoned the House -Judiciary Subcommittee on Monopolies and Commercial Law recently, his calls were not returned. When he called again two hours later, the staffer told him: ''I was -hoping you'd call back. I can't make any long-distance calls.''
How long will the ban be in effect? ''Until Jan. 3, when we get our budget for next year,'' the staffer said.