FRANKFURT, March 22 — After two years of emotional debate that cut to the heart of questions about German identity, the upper house of Parliament passed a groundbreaking immigration law today that would open the gates to greater numbers of skilled foreign workers.

Or so it seemed. The vote was close, and politicians from the pivotal state, Brandenburg, which has a coalition government, did not follow the voting procedure laid down for such governments. The center-right Christian Democratic Union therefore denounced the outcome as unconstitutional and vowed to appeal to Germany's high court.

But even before the vote, the law had become an election-year battle between Chancellor Gerhard Schröder, a Social Democrat, and his conservative challenger, the Bavarian premier, Edmund Stoiber.

Hoping to lure conservatives, Mr. Schröder spent months haggling over details and made compromises that diluted the law's impact. Although one of its basic goals was to attract greater numbers of skilled foreign workers, the preamble now says that the purpose is to "regulate and limit" the flow of immigration.

The bill would make it harder for people to gain political asylum, and cut back on benefits for those who get it. It would also prod immigrants to become more "integrated" in German society.

If the new law survives constitutional scrutiny, however, it will represent a historic turning point in the way Europe's most populous nation copes with one of its greatest insecurities.

For decades, even when Germany recruited millions of "guest workers" in the 1950's and 1960's, German leaders insisted that theirs was not "an immigration country" and made it nearly impossible for foreigners to become citizens. Now, with more than seven million resident foreigners, or 9 percent of the total population, Germany is already a nation of immigrants. These include lifelong guest workers and their children, people from Central Europe and Russia who claim German ancestry, asylum seekers and thousands of illegal immigrants.

The law is also an attempt to reconcile Germany's conundrum: though unemployment here is nearly 10 percent, employers complain about increasingly acute shortages of skilled workers. Given Germany's low birth rate and aging population, demographers expect widespread labor problems by 2010.

By some estimates, Germany will need 450,000 more workers a year to support the growing number of retirees. A bipartisan commission on immigration led by Rita Sussmuth, a leader in the Christian Democratic Union, recommended admitting an additional 50,000 people annually.

Because Germany is a member of the European Union, citizens from the other 14 member countries already have automatic permission to live and work here. The new law would allow companies to recruit workers from outside the European Union, if recruitment would not undermine the demand for local workers.

The law also tries to promote the cultural "integration" of long-term foreign workers, who would be allowed to bring children only younger than 12, for example, so that the children would be more likely to attend German schools and learn the language.

Despite the strong support from business groups for expanded immigration, opposition leaders in the conservative Christian Democratic Union and the Christian Social Union insisted that the new law would open too many opportunities to foreign job seekers.

"We need and we want a reform of immigration rights, in the competition for the best heads," said Mr. Stoiber, who is challenging Mr. Schröder for the chancellorship in September. "But we do not want an expansion of immigration as a whole."

In today's 35-to-34 upper house result, which may well be struck down as illegal, the crucial vote came down to the state of Brandenburg, which has a coalition government of Social Democrats and Christian Democrats. Coalition members are supposed either to agree on their vote or abstain, but Brandenburg's premier voted for the law, and its interior minister voted against it.

The president of the upper house, the Social Democratic mayor of Berlin, ruled that Brandenburg had voted for the law. Opposition leaders said they would appeal to the nation's constitutional court.