At Phoenix Laser Systems, a San Francisco firm that makes precision instruments for eye surgery, executives say the immigration law passed by Congress late last month opens the door to recruiting many more highly prized scientists from Poland, Czechoslovakia and the Soviet Union. Only there has the company been able to find scientists with backgrounds in physics, engineering and biomedicine needed to design its laser product.

"That {law} will be extremely helpful," said Alfred Sklar, the company's director of research. And because the company plans to expand its operations next year, "there will be a need."

Mo Sussman, co-owner of the Connecticut Avenue NW restaurant Joe & Mo's, is worried about a less-noticed section of the new legislation, a provision that will cut back the number of lower-skilled workers granted visas each year.

Restaurants, hotels, poultry processing plants, health care institutions and professional couples needing at-home child care rely heavily on immigrant workers. In the kitchen of Sussman's restaurant, for example, only three of 19 workers are American-born, he said.

"I am an American restaurant. I serve only American wines. I'd love to hire Americans. But I can count on one hand how many American dishwashers we have," Sussman said. If he is forced to illegally hire undocumented immigrants because of the new law, he added, then "the government has taken another notch in making me an outlaw."

As its sponsors envisioned, the sweeping revision of immigration laws approved by Congress will have a major impact on the labor market. But critics say the effects will be uneven and mixed.

The bill calls for a dramatic increase in the number of visas granted on the basis of job skills -- from 54,000 visas annually to 140,000. The bulk of these additional visas will go to professional and skilled workers. The number of visas available for lower-skilled workers will shrink from about 18,000 annually to 10,000.

High-tech businesses are waiting eagerly to bring into this country tens of thousands of highly skilled foreign workers, with the expectation that the new labor pool will prevent shortages and spur innovation and economic growth. But in low-skill industries, where a tight labor market has meant heavy reliance on immigrant workers, employers say a reduction in the number of visas for less-skilled immigrants could be devastating.

"In certain parts of the country, there is a severe labor shortage for lower-skilled workers," said Christopher Teras, an attorney for poultry and other industries that rely on foreign-born labor. "I think a lot of employers are going to be surprised at how seriously they are going to be affected."

Supporters of the legislation, many of whom sought the shift toward skilled and educated workers, acknowledge what they call "the nanny problem" but defend the final product.

"I think we've struck an important balance," said Rep. Bruce A. Morrison (D-Conn.), sponsor of the House bill. "I think we've taken an appropriately moderate course in not cutting off completely {the unskilled workers} but focusing most of the visas on people with skills."

The new legislation, which has the support of President Bush, overhauls regulations governing legal immigration established 25 years ago and raises by nearly 40 percent the number of people allowed to enter the United States each year.

The revisions will have a broad effect, ending the threat of deportation for Salvadoran refugees, making it much easier for family members to join recent immigrants here, permitting a significant increase in the number of immigrants from Western European countries and removing McCarthy-era restrictions that barred entry on the basis of ideology and homosexuality.

The provision regulating lower-skilled labor is not the only avenue for these workers to enter the country. The law also expands the number of visas set aside for several European countries -- visas that could go to immigrants who will ultimately work as baby sitters or manual laborers.

But critics argue that that is still not enough and point to the unmet demand now in many of these occupations. The demand is also evident in the number of employers seeking "certification" from the Labor Department to hire foreign workers, a process through which a person may secure a visa when it is deemed that no qualifed American is available for a job.

More than 24,000 of the 60,000 "certifications" granted annually are for unskilled workers, according to Labor Department figures. But because of the informal cap on visas for lower-skilled immigrants, people must wait years for their documentation after they are certified. The reduction to 10,000 such visas for workers and their families will make that wait longer.

"It's going to be hopeless," said Caroline Killea, an immigration attorney for professional women hiring foreign baby sitters. "The home-care situation here is already so tight."

The current waiting period -- from when an employer applies to hire a foreign worker to when a visa is granted -- is three to four years, she said. That period could grow to 10 years, making immigrants less likely to view such jobs as a means of securing visas.

With the new restrictions on visas, said Killea, "you're cutting out your labor pool."

The decision to set aside most of the visas for skilled and professional workers reflects a "philosophical judgment on which there was widespread agreement," said Demetrios Papademetriou, director for immigration policy and research at the Labor Department.

"Some would say" the availability of visas for unskilled workers "is a subsidy to maintain the viability of low-wage industries" that allows those companies to continue paying wages too low to draw American workers, Papademetriou added.

Overall, the immigration legislation -- the most comprehensive rewriting of laws governing legal immigrants since 1924 -- has been hailed as a boon to the American economy.

"From the business perspective, it's a dramatic improvement," said Harris Miller, coordinator of a coalition of businesses formed to promote changes in immigration law. The business community fought for and won numerous provisions that will make it easier to hire and keep foreign workers.

Gregory Fossedal, vice president of the American Immigration Institute, a pro-immigration research group, praised the bill as a whole but bemoaned the restriction on lower-skilled workers.

"There's this fallacy that certain types of economic activity are good and . . . that other types are bad," he said. But a low-skilled worker providing child care makes it possible for professionals such as attorneys and physicians to work, he added.

"The economy fits together like a matrix."