DETROIT (AP) _ Negotiators for Detroit Newspapers have canceled this week's contract talks with striking unions, saying they must focus on U.S. Justice Department questions stemming from a union complaint.

Tim Kelleher, senior vice president of Detroit Newspapers, said the company was told Monday by the Justice Department that it wants a response by the end of the week.

The unions filed an antitrust petition last month questioning the legality of the Detroit Free Press and The Detroit News publishing a combined paper.

Under a joint operating agreement implemented in 1989, the Free Press and News publish separate newspapers Monday through Friday and combined weekend editions. Since the strike began July 13, they have published a joint daily edition put out by managers, replacements and employees who have crossed the picket line.

Detroit Newspapers, which runs the Free Press' and News' noneditorial operations, said it informed the Justice Department in 1992 of plans to publish joint editions in the event of a strike.

Negotiations had been scheduled this week with unions representing pressmen, Teamsters and mailers.

Also Monday, Detroit Newspapers' request for a court order limiting picket activity at its Sterling Heights printing plant was reassigned to a new judge. The judge who drew the case last week is tied up with a murder trial.

Police said Monday they would support management's call for a court-ordered limit on the number of pickets.

Chief Thomas Derocha held a news conference Monday to discuss what he called lawlessness by pickets Saturday night at the plant, where between 1,500 and 2,000 union supporters rallied.

While the crowd was generally peaceable, he said, some demonstrators illegally blocked vehicles from entering and leaving the plant where the combined strike editions of the newspaper are printed.

Police support for an injunction is not a surprise, said AFL-CIO strike support organizer George Curtin.

``They've been working hand and fist with the newspaper management right from the start,'' Curtin said. ``They have not been neutral.''

The company used helicopters Saturday night to carry some of the 1 million Sunday newspapers from the plant.

Six unions are on strike over wages, work rules and what they call unfair labor practices by the News, owned by Gannett Co. Inc., and the Free Press, owned by Knight-Ridder Inc.