WASHINGTON — Illegal immigrants are increasing despite tighter border security and now outnumber foreigners moving to the United States legally, according to a new report.

The report yesterday by the Pew Hispanic Center said that immigration in general has been picking up, tracking the reviving U.S. economy and improving jobs picture.

"The U.S. economy was obviously a very important factor in determining these flows," said Roberto Suro, director of the center and a co-author of its study, which documents immigration levels from 1992 to 2004, generating estimates from a variety of U.S. census data.

Immigration — both legal and illegal — topped 1.5 million people in 1999 and 2000, according to the report. The number of people entering the United States then fell to 1.1 million people by 2003, the same level as in 1992.

Immigration bounced back to 1.2 million in 2004, but the report cautioned that it is difficult to say whether the recent upswing is part of a new trend.

"The extremely high (immigration) flows at the end of the past decade were not the norm, nor part of a long-term trend, but rather the peak of a momentary increase that lasted for only a few years," said the report, which was written by Suro and demographer Jeffrey Passel.

The Pew Hispanic Center is a nonpartisan research organization supported by the Pew Charitable Trusts.

Border security gained national attention last month after the governors of two states, Arizona and New Mexico, declared states of emergency on their borders with Mexico. The governors cited security shortcomings by the federal government.

Homeland Security Secretary Michael Chertoff said at the time that he had already ordered a review of border-security strategy.

"The Pew report is yet another indicator that the immigration system is broken," said a statement by Sen. John Cornyn, R-Texas, chairman of the Senate's immigration, border security and citizenship subcommittee. "Immigration reform must be comprehensive and address both enforcement and improved avenues for legal immigration."

Cornyn has co-authored a bill that would create a temporary worker visa, as well as a mandatory system for employers to check on the immigration status of prospective employees.

More than 34 million immigrants now live in the United States, and make up 12 percent of the nation's population, according to a Census Bureau estimate last year. The number has more than tripled since 1970, when the foreign-born population numbered 9.6 million.

The Pew report said immigration levels closely mirror economic conditions in the United States — as the economy improves, immigration increases — suggesting that the lure of jobs is a strong factor in attracting people to this country. The U.S. economy appears to be a stronger factor than economic conditions in the countries sending immigrants here, the report said.

Among the report's findings:

• Since 2001, the number of legal permanent residents entering the United States has declined from 578,000 to 455,000, while the number of illegal immigrants has increased from 549,000 to 562,000. Legal, temporary residents account for the remainder of people entering the country.

"We've seen a fairly steady growth in the number of undocumented immigrants living here, and this data shows very sizable numbers coming in," Passel said.

Declines in legal immigration "appear to reflect processing backlogs, security delays and other developments that followed the Sept. 11 attacks," the report said.

• Mexico accounted for about a third of all U.S. immigrants, a percentage that was steady from 1992 to 2004. Other Latin American countries accounted for about 20 percent of all immigrants, Asia accounted for a little more than a quarter, and Europe and Canada combined to account for about 14 percent.

• More immigrants are shunning states with large immigrant communities, such as New York and California, and moving to states with smaller foreign-born populations, such as North Carolina and Iowa.

Material from The Washington Post is included in this report