RESEARCH INTO Census data shows three crucial things about Baltimore:

The city's declining population is not an aberration but a problem shared by most cities like it.

The only way similar cities have halted their population decline has been through immigration.

Baltimore is the first city to seek to address this issue with a proactive approach.

Baltimore has been steadily losing population for half a century, roughly 1 percent a year since World War II. Like sand running through an hourglass, that means fewer jobs, lower property values, empty neighborhoods, decline that feeds on itself. The official Census figures show the city population dropping 11.5 percent even as the region gained more than 10 percent. Baltimore is the hole in the doughnut.

Our research, funded by the Abell Foundation, has found that there is only one way to stabilize Baltimore's population: immigration. The experience of every comparable American city shows that without immigration from abroad, these cities shrink in population. There are no cities that grow only by attracting people from other states.

All cities with a substantial flow of immigration are gaining population: New York, Los Angeles, Chicago and Houston. Cities without a substantial flow of immigrants do not grow: Philadelphia, Detroit, Cleveland, Milwaukee. And all cities that decline in population lack a substantial level of immigration: Pittsburgh, Buffalo, St. Louis.

Washington, to which Baltimore has recently been unfavorably compared, is more like Baltimore than it is different. Its population declined in the 1990s, and most recent immigrants have chosen the suburbs, rather than the city, in which to settle.

Cities that are most like Baltimore tell the tale. Since 1990, Boston has reversed its decades-long population slide and has begun to grow because of immigration. Oakland, Calif., in which whites are a minority, is a growing city because of immigrants. Newark, N.J., another city like Baltimore in which African-Americans are the majority, stabilized its population between 1990 and 2000 because of a substantial influx of immigration.

So Baltimore needs immigrants.

Those cities that benefited from immigration had done nothing affirmative to achieve it. They were lucky. And once substantial immigration starts, it is self-sustaining.

What is important is that Mayor Martin O'Malley and his administration are taking an affirmative approach to addressing the problem. Mr. O'Malley gets it better than most because he wants to base his solution to the problem on data, on how immigration really works to renew cities, and not conjecture. He also wants to build public support for a strategy based on that data.

If you can't measure something, you can't improve it. No city has ever done what Baltimore now has the opportunity to do. It can attract and retain immigrants through a deliberate approach that starts in city neighborhoods and extends to changing national policy rather than simply reacting to an increased flow of immigrants if they happen to come.

While Baltimore can learn from good programs in New York, Boston and Minneapolis that welcome immigrants who have already come, to credit these programs for the influx is like praising the rooster for the dawn.

Examining these three cities in detail, along with dozens of other programs, we found that they simply reacted to a flow of immigrants that began for other reasons. No city, no state, has created a substantial flow of immigrants as a policy. In fact, when advocates began to publicly speculate about Iowa creating an "Immigrant Enterprise Zone" about two years ago, Gov. Tom Vilsack had to publicly disown the idea. The state hadn't done its homework.

How can Baltimore attract immigrants?

First, by doing its homework, literally. Census data show that immigrants have a range of motivations for settling in a community, no different from anybody else. Family, employment, education and housing are key. In theory, there is a chicken- or- egg problem. You don't get a Central American neighborhood without a Central American grocery. But you don't get a Central American grocery without Central Americans, either.

That is the supply side of the equation.

The magnets will vary for each group targeted. Some will be best attracted as foreign students. Some will be recruited for high-skilled jobs. Others will just need to know that their skills will find interested employers. In short, jobs are key.

But housing to keep them in the city will also matter, as will schools responsive to their kids, and city police and other services that reach out to them. In the longer run, the city can join with others to pursue changes in immigration law to make cities such as Baltimore more competitive in the immigrant supply system.

That's why the O'Malley administration is in the right place to take the appropriate steps. And the people of Baltimore can help themselves by helping him. Baltimore's future renewal based on a flow of immigrants will start with building a consensus within Baltimore based on the evidence: Without a greater flow of immigrants into the city, Baltimore cannot and will not grow.

Nobody will benefit more from new people in Baltimore's old neighborhoods than the current residents of Baltimore.

Bruce A. Morrison is a former Democratic congressman from Connecticut. Paul Donnelly researches and writes about immigration and citizenship.