Four years after ordering the city’s Police Department to make do with less because of fiscal woes, Mayor Bloomberg announced yesterday that he is earmarking $33.8 million next year to boost the department with 1,200 new hires.

Mr. Bloomberg’s announcement comes at a time when the murder rate is at a historic low and the NYPD is doing double duty responding to crime and running a sophisticated counterterrorism operation.

“I don’t want to wake up and find crime going up and then have to build up the Police Department,” Mr. Bloomberg told reporters at City Hall.

As the first major expansion since 1993, the increase will take the number of uniformed police employees to 37,838, still leaner than the police department’s 2003 force of 39,110.

The two-phase hiring will include 800 new police officers as well as 400 civilians who will free up the same number of officers on desk duty for patrol. It comes as other agencies are still paring down and after political opponents chided Mr. Bloomberg for skimping on security.

Mr. Bloomberg cited the city’s growing population as the rationale for hiring more officers. The decision makes clear that he is not willing to risk a possible slip in crime numbers that he so often points to in talking about how well the city is doing. Last year the city had 540 homicides, the lowest number since 1963.

Rep. Anthony Weiner, who campaigned against Mr. Bloomberg last year, called it “welcome news after a 12% decrease in operational strength since 9/11.”

The number of police officers on the street has dropped by about 4,000 since the World Trade Center attacks in 2001. Of that, 3,000 officers were lost to attrition, while 1,000 were deployed to counterterrorism work. Police Commissioner Raymond Kelly said the new officers would be assigned to precinct patrol.

“We have a lot on our plate, so the mayor’s decision today makes it all a lot easier to digest,” he said.

Sources said the timing was likely linked to word that the city might be able to tap into federal homeland security money. Mr. Bloomberg said beefing up the department is a “smart investment” that would help the city “lock in” the low crime rates and spur more tourism and economic activity. He said the city might be able to cover some of the cost, which is expected to rise to $80 million by 2010, with federal money, but that there are no guarantees.

The speaker of the council, Christine Quinn, and the chairman of the council’s Public Safety Committee, Peter Vallone Jr., praised the move.

“The department was being stretched past its limits,” he said. “An increase in the size of the department is absolutely necessary.”

The PBA president, Patrick Lynch, called the move of 400 officers from desk duty a “Band-Aid” approach to getting “sorely needed police officers on the street.”

“With nearly 3,000 members quitting or retiring each year, the NYPD recruitment effort is struggling to keep up with attrition,” he said. “Unless New York City makes a police officer’s top pay competitive with other law enforcement agencies, they simply will not get enough good quality candidates.”

Other Patrolmen’s Benevolent Association officials said they saw the new hires as the first admission that the department is stretched too thin. The new recruits will be hired in two phases. The first 400 uniformed positions will start the Police Academy in July and the second half will come in January 2007.