A D.C. Superior Court judge yesterday at least temporarily blocked the city from enforcing a provision of its new contract with the International Brotherhood of Police Officers that would allow the union to collect fees or dues from officers who are not members of the union.

Judge Peter H. Wolf granted a request by the Fraternal Order of Police, arival union seeking to dislodge the IBPO as the authorized bargaining agent for the city's police officers, and ordered the city to stop any preparations it was making to deduct the dues. Under the three-year contract negotiated between the city and the IBPO last month, the city had agreed to deduct $5.50 every two weeks in dues or fees from the paychecks of about 3,000 city police officers.

Wolf's order will remain in effect until a preliminary hearing on the case Aug. 4. City officials said they must begin paperwork no later than Aug. 8 in order to deduct the money from paychecks on Aug. 21.

Lawyers for the FOP argued that the contract allowed an involuntary union fee deduction only if two-thirds of the officers authorized such deductions. FOP attorney Robert E. Deso said that only about 56 percent of the officers were members of the IBPO at the time the contract was signed July 15 and more than 350 other officers have resigned from the union since then.

City officials argued that under the terms of the current contract, union members can only withdraw in March and September, so that the July withdrawals are not valid. The city argued that two-thirds of the police officers were in fact still paying dues to the union as of July 15.

Wolf said that there was a "substantial likelihood" that the FOP would be successful in a court hearing and that there were "serious legal questions" about the city's and the IBPO's agreement to deduct the dues from nonunion officers.

The 90-minute hearing was only one part of the lengthy skirmishing between the two unions. The FOP has also filed an unfair labor practice complaint against the D.C. government for allegedly denying officers the right to not join a union.