There are plenty of opinions about how many officers the D.C. police ought to have.

D.C. Council member Jack Evans (D-Ward 2) says it should be 4,000 — and 4,200 would be better. Police Chief Cathy L. Lanier says the city needs at least 3,800, lest there be trouble. Kristopher Baumann, head of the city’s police union, also sets the thin blue line at 3,800 officers. D.C. Council member Phil Mendelson (D-At Large), whose committee oversees the police department, is right there with him.

The staffing issue has come to a head of late because the city is in its toughest fiscal crunch in 20 years, and as Mayor Vincent C. Gray (D) tries to juggle funding for education, transportation, human services and more, the police department isn’t getting the kid-gloves treatment it’s gotten in recent years.

Under Gray’s budget proposal, the force, now about 3,880 sworn officers, would dip under 3,600 by September 2012. That level of policing — about what the city had in 2001 — has stoked crime concerns that have bordered on fearmongering.

A local columnist recently said the city would be risking a summer “blood bath” should the number of officers fall much below what we have. Mendelson and Evans are working to add more recruits to the budget before it passes this month.

But if you assume the formula is more officers equal less crime, it’s not that simple. “It is more art than science,” said Ed Maguire, an American University criminology professor who has studied police staffing.

In 2000, Maguire and a colleague reviewed no fewer than 27 studies that attempted to link the size of a police force with crime rates. Almost half of the studies found no relationship between the two. Of the remainder, more found that crime increased as police levels rose.

What tends to drive police staffing is revenue, rhetoric and custom as much as crime.

“I have visited a lot of police departments in my life. I can’t remember ever visiting one that didn’t say they needed more cops,” Maguire said. “There are places in the country that are understaffed; there is no doubt about that. There are also places in the country that are overstaffed and probably a whole bunch that are just about right where they belong.”

That’s not to say that adding officers is a bad idea. But there are often more important determinants of public safety than the number of police officers per capita — poverty levels, education levels, the economy, population density, income inequality. That’s one reason why there is no national standard for police staffing.

What ends up determining police hiring is, for better or worse, the seat of one’s pants. “There’s no magic formula,” Lanier said last week on WAMU (88.5 FM)’s “Politics Hour.” Her 3,800 figure, she said, is “based . . . on 21 years of policing here.” She looks at calls for service and public satisfaction with the police department and, yes, crime statistics. “All of those things tell me that right now we’re okay,” she said.

Baumann, who has been with the department for a decade, also relies on his firsthand experience. He says that with 3,800 officers or fewer, investigators get put on patrol, and those who are on patrol do less beat-walking and more speeding from call to call in their cruisers.

Politicos tend to be even less scientific.

“My sense, my intuition, is that we function best with about 4,000,” Evans said.

“There’s been a level of comfort with a police force of 3,800 or more,” Mendelson said.

What gets lost in these discussions isn’t the number of officers, but their productivity. In a city government — and an economy at large — that has found ways to get more work out of its employees, are police officers any different? “The last 20 years of criminology has taught us it’s really what you do with your cops that counts,” Maguire said. “There are wasteful ways of using police, and there are efficient ways of using police.”

There’s no doubt that the D.C. police department has gotten more efficient since the force had 4,800 officers or more in the early ’90s. The rise of statistical analysis has improved deployment; new computer systems, including laptop computers in every patrol car, have helped with paperwork. But while other police departments regularly hire consultants to study how to improve staffing, the D.C. police haven’t done a study in “years,” Mendelson said. (A council bill that would have authorized a study died this week.)

That leaves the politicians figuring out staffing out for themselves. For D.C. Council member Tommy Wells (D-Ward 6), it was the “ring of steel.” That’s what Lanier called it when, after eastern Capitol Hill had a carjacking problem in 2008, she flooded the neighborhood with officers and police cars. It got the job done.

Wells wants to make sure there still can be rings of steel. “I don’t know how low we can get,” he said, “but I don’t want to find out.”