NEW YORK — About 11.7 million immigrants are living in the United States illegally, a population that has not varied much over the last three years but showed signs recently of increasing again, according to estimates published Monday by the Pew Research Center Hispanic Trends Project.
As lawmakers in Washington consider an immigration overhaul that could include a pathway to legal status or citizenship for millions of unauthorized immigrants, the figures from the nonpartisan Pew Center are regarded by many demographers as the most reliable estimates of the number of immigrants who might be eligible for those programs.
The new estimates, which are based on the most recent census data and other official statistics, show that the population of immigrants here illegally did not decline significantly from 2009 to 2012.
That result occurred despite record numbers of deportations by the Obama administration — about 400,000 each year — and laws to crack down on illegal immigration in such states as Alabama, Arizona, and Georgia.
Recent figures, including reports from the US Border Patrol of illegal crossings at the Southwest border, suggest that the numbers began to grow again last year. But Pew researchers said the increases in the 2012 census data — the latest available — were too small for them to conclusively confirm the recent rise.
Overall, the hopes of some lawmakers that tough enforcement could substantially reduce the numbers of illegal immigrants are not borne out by the new estimates.
“For Congress working on the demands of a potential legalization program, these are pretty solid numbers,” said Jeffrey S. Passel, senior demographer at Pew’s Hispanic Trends Project, who helped write the report.
The new numbers come as prospects for passage of a comprehensive US immigration bill appear dim because of strong opposition in the House.
A bill passed by the Democratic-controlled Senate and backed by the White House includes billions for border security and a 13-year path to citizenship for the 11 million immigrants already here illegally.
But most House Republicans have rejected this comprehensive approach, and the House Judiciary Committee has moved forward with individual, single-issue immigration bills that could come to the floor sometime later this year or next.
It’s unclear whether the GOP-dominated House will ever pass legislation that could form the basis for a final deal with the Democratic-controlled Senate.
In parts of the country, public opinion on illegal immigrants has shifted in favor of granting legal rights. This year, some state legislatures passed pro-immigrant measures such as college tuition breaks and rights to driver’s licenses, although others enacted laws aimed at tightening the system.
For the first time, the Pew researchers used larger census samples from past years and went back to revise some previous estimates. The new figures, while only slightly different, show an even clearer picture of the surging growth in unauthorized immigrants to a peak of 12.2 million in 2007 from 3.5 million in 1990.
In 2008 and 2009, there was a steep drop, with the numbers falling to an estimated 11.3 million. After 2009, the population leveled off and by some measures might have been gradually growing.
The Pew report does not point to any causes of the population changes. But Passel noted that the dates of the decrease matched the onset of the deepest years of the recession.
“We don’t know what caused that decline, but it certainly coincides with the recession,” Passel said. “And we can say that the current enforcement practices have not led to any measurable reduction beyond the 2009 period.”
The Pew report also confirms a striking reversal in the patterns of migration from Mexico. Since 2007, Pew demographers found “dramatic reductions in arrivals of new unauthorized immigrants from Mexico.” They cite Mexican census figures showing that the rate of migration to the United States dropped by two-thirds from 2007 to 2012.
From 2007 to 2009, the report says, more undocumented Mexicans left the United States than came here illegally, “a marked change in pattern from the largest immigration wave in US history.”
About 6 million immigrants born in Mexico still make up 52 percent of the unauthorized population, according to the Pew estimates.
But recent increases in illegal arrivals are migrants from countries other than Mexico, including Central American nations.
Roughly speaking, Passel said, the number of migrants coming in illegally and those leaving the United States or gaining legal status are now in balance.
The report shows variations among states.
In Texas, the unauthorized population never saw any significant decline.
In Florida and New Jersey, the numbers are growing again after falling in the first years of the recession. In California, Illinois, and New York, the numbers declined after 2007 and never rebounded.