The Justice Department on Wednesday waded into a federal trial over the New York Police Department’s stop-and-frisk practices, strongly endorsing a monitor to oversee changes if a judge were to find the practices to be unconstitutional.

But the so-called statement of interest, which the department filed late Wednesday in Federal District Court in Manhattan, stopped short of offering the Justice Department itself as a monitor for the Police Department.

The Justice Department lamented that the court had decided to address questions of fact — whether the department systematically violated New Yorkers’ rights — and the question of remedies at the same time, saying it would have preferred to weigh in only after the former had been decided.

In its carefully worded 21-page statement, the Justice Department took no position on matters of fact in the case. But should the court find against the city, the Justice Department said, it would endorse the use of a court-appointed monitor. “The experience of the United States in enforcing police reform injunctions teaches that the appointment of an independent monitor is a critically important asset,” the department said.

The statement added: “A court-appointed monitor in this case would help the court ensure that, if any pattern or practice is found to exist, it is effectively and sustainably remedied.”

The judge in the case, Shira A. Scheindlin, is set to decide in the coming months whether such violations existed in the Police Department’s tactic of stopping, questioning and frisking New Yorkers.

The trial, which ended in late May after two months of testimony, has emerged as a flash point in the mayoral race, with candidates drawing stark lines over whether they would embrace the tactics, strongly associated with Mayor Michael R. Bloomberg, or seek to end them if elected.