Long a poster child of high crime, Oakland is preparing to lay off nearly a fifth of its police force just as it has turned the corner on crime, part of a national trend in the recession.

This city of 400,000 said last month it would cut 140 officers from its 800-strong police force, the department's first-ever mass layoffs.

Oakland police faced demonstrations in January after a transit police officer shot an unarmed man to death. The city is planning to lay off nearly 20% of the department's officers as it tries to erase a budget deficit.

Dozens of hard-hit cities have done the same. In May, Toledo, Ohio, laid off 11% of its police force. In Minnesota, seven city police departments have closed since March, and state officials say an additional nine departments are likely to close by year's end.

The Oakland cuts, to take effect in September, come after the city spent the past five years building its police force to the highest number of officers it had ever seen. The buildup is credited with helping to lower the city's number of homicides by about 20% and cut its violent crime by about 13% over the past year.

To hang onto those gains, Oakland has tried for months to protect police from cutbacks. Faced with an $83 million budget deficit, Oakland lawmakers instead closed City Hall one day a month, trimmed the city attorney's budget 10%, reduced Mayor Ron Dellums's staff by 20% and even grounded the police department's helicopter, saving the city about $400,000 annually.

But the moves weren't enough. "We absolutely don't want to lose any police officers, and under no circumstances would we do this voluntarily," said Oakland City Council president Jane Brunner. "But we have no other choice. Our hand has been forced."

Oakland's experience shows how the recession is pushing some cities to enact last-resort budget cuts that could threaten basic law and order.

Police layoffs have been particularly prevalent recently in California, which has the second-largest number of local police at about 40,000 officers, according to the Department of Justice. New York state has the largest, with about 50,000 officers. Stockton, Calif., announced last month it would lay off just less than 10% of its police force, while Modesto, Calif., plans to shed 5% of its officers.

California's budget crisis is exacerbating the financial pressure on communities.

Overall, about 1,100 police officers lost their jobs in California in the fiscal year ended June 30, and an additional 900 are projected to be laid off in the current fiscal year, according to the California Association of Police Chiefs. One city bucking the trend is Los Angeles, which has proposed hiring 1,000 officers by year's end, despite facing a $530 million budget deficit.

In Oakland, law and order is a particular focus because the city wants to eradicate its reputation for violent crime, which has hurt its economic prospects. For most of this decade, Oakland had a crime rate that was double or triple the national average, according to Federal Bureau of Investigation statistics and a report by former Oakland police chief Wayne Tucker.

Even this year, despite an overall drop in crime, Oakland has seen some high-profile violence. In January, the city grappled with riots over the killing of an unarmed man by transit police. In March, a parolee shot and killed four police officers.

Still, the growth in Oakland's police force helped tamped down crime, statistics show. "It's a big deal that we've been able to bring the crime rate down, and part of that can be attributed to adding more cops to our department," Ms. Brunner said.

Barry Donelan, vice president of the Oakland Association of Police Officers and a sergeant on the force, said the department was trying to negotiate with the city to find areas where it could help avoid layoffs. "Laying off the number of officers [the city council] is proposing will have a major impact on crime, and it will not be positive," he said. "The city and its residents will suffer." He declined to comment on the morale of the police officers.

"The prospect of losing officers is not something we look forward to, but it's an unfortunate sign of the city's fiscal situation," said Jeff Thomason, spokesman for Oakland's Police Department.

To blunt the pain, Oakland officials have applied for about $24 million from a $1 billion federal grant offered by the Department of Justice that is part of the economic-stimulus plan. The grant, called the Cops Hiring Recovery Plan, was slated to save about 5,500 police jobs.

But city lawmakers are concerned they won't receive much of the stimulus money because there is so much competition for the funds. In late June, Mr. Dellums traveled to Washington to lobby for the grant dollars, visiting with Attorney General Eric Holder and others.

"We desperately need the federal government to assist us to the maximum extent possible," Mr. Dellums said.