The reforms include changing policies on stun guns and on shooting at moving vehicles, repealing questionable laws and carrying out new guidelines for stops and searches by local law enforcement. The city must also hire an independent monitor to ensure that the changes are enacted properly.

When federal officials and the city announced the accord in late January after several months of talks, they did so with optimism that the city was turning a new leaf and setting a national example for change. About a year earlier, the government had released the scathing results of an investigation that found that Ferguson’s law enforcement system regularly violated people’s constitutional rights and used its police and courts to make money rather than ensure public safety. The investigation unfolded in the wake of the fatal police shooting of 18-year-old Michael Brown, after complaints from the predominantly black population of Ferguson and surrounding communities that the police regularly harassed them.

But after the Council held several public hearings, members started to waver. While many in the community urged the Council to pass the agreement, others expressed concern that its cost would bankrupt the city. Ferguson’s finance director, Jeffrey Blume, said enacting the agreement would cost as much as $3.7 million in the first year and $3 million in subsequent years. Yet others argued that challenging the agreement would lead to a court battle that one lawyer for the city estimated would cost as much as $8 million.

The city has been running an operating deficit of about $2.5 million a year since the Brown shooting, which led to widespread demonstrations and unrest.

The Council voted a little more than a month ago to send the agreement back to the Justice Department with seven amendments, even though federal officials had said they would sue if the city did not approve the consent decree in its entirety. The Justice Department did just that, filing a lawsuit the day after the Council’s vote.

But Ferguson officials started showing signs of a change of heart about a week ago after the Justice Department sent them a letter saying it would work with them to keep the costs of the changes in check. To help cover the costs of the agreement, the city has placed tax increases on the ballot next month.

“The federal government now, and their monitor, will oversee and watch and report back on the progress we’ve made,” Mr. Knowles said in an interview. “This is no longer me sitting at a meeting saying, ‘Look at all the stuff we did,’ and people saying, ‘Ah, you’re lying.’ That will really help us get past that level of distrust.”