MEXICO CITY (AP) _ Mexico City's police chief stepped down Friday after battling for nine months to stem a wave of kidnappings, robberies and slayings in this city of 8.5 million.

Rodolfo Debernardi's tenure as public safety secretary was marked by harsh press criticism, and a constant series of highly publicized cases tarnished law enforcement efforts.

Former prosecutor and university professor Alejandro Gertz Manero, 59, stepped into the job, taking on one of the most thankless police jobs in the hemisphere. The police force is so riddled with corruption that army troops replaced police in some neighborhoods in 1997, and dozens of policemen have been charged in rapes and murders.

Contrasting with Debernardi, who like many of his predecessors was a retired military officer, Gertz Manero pledged to act ``fundamentally as a representative of civilian society'' in the fight against crime.

Before his appointment, Gertz Manero headed a civilian commission that consulted on law enforcement issues in Mexico City, a job he said puts him in good stead to build citizen participation.

Gertz Manero pledged to give police ``substantial increases in wages ... immediately.''

``The concept of a poorly paid policemen, exploited and subject to extortion by their superiors, should end today,'' he said, referring to complaints by officers that they must pay bribes to superiors in order to work, carry guns or drive dilapidated patrol cars.

Mexico City has suffered a four-year crime wave. An average of 700 crimes involving weapons were committed every day in 1997, resulting in six deaths daily. Crime has driven away business and led to travel warnings by the U.S. Embassy.

Debernardi was appointed in December, 1997 by left-center opposition Mayor Cuauhtemoc Cardenas, the city's first elected mayor in seven decades.

Three months after taking office, Cardenas said policing had improved under his administration, with arrests made in one of every three robberies, compared to one out of 14 in 1997.

But high-profile cases _ included deadly muggings in city taxis in which Americans and other foreigners were sometimes the targets _ hurt police efforts.

Debernardi was subject to constant sniping from the press and city legislature, especially for his claims that crime rates were declining when most crime categories appeared to increase or remain at the same high levels.

One of the most damaging moments for Debernardi came in July, when prosecutors charged nine policemen with luring three teen-age girls into a squad car, imprisoning them at a police stable for four days and raping two of them.

Debernardi will continue to work with city law enforcement in an unspecified capacity, city officials said.