Washington -- Silicon Valley tech companies for years have urged Congress to "staple a green card" to every master's degree or Ph.D that a foreign student earns in science, technology, engineering or math at a U.S. university.

The giant immigration overhaul now moving through the Senate Judiciary Committee would do just that, with the intention of attracting the world's "best and brightest" to U.S. shores.

But like many past changes to immigration law, this one could have unforeseen consequences, critics warned, potentially turning U.S. universities into "green card mills" and providing a large new pipeline to permanent residency for foreign graduate students, at the same time discouraging Americans from entering the very fields where they are claimed to be in short supply.

"What it's going to do is induce universities to start selling green cards through their master's programs," said Ron Hira, an associate professor of public policy at Rochester Institute of Technology in New York. "A master's program could be as short as 12 months. What you actually end up doing, I think, is creating very large flows of people who see a master's as a fairly inexpensive way to basically buy a green card."

The bill sets no cap on the number of these potential new green cards. It sets no quality standards for the degrees or for the universities and colleges that would grant them. It bypasses the usual requirements that employers seeking green cards for their workers demonstrate that they have sought U.S. workers first.

Less attention

The green-card proposal has drawn far less media attention than the bill's plan to nearly double, and potentially triple, the number of H-1B temporary visas for skilled workers, a controversial proposal that divides both parties and is the subject of intense maneuvering behind the scenes.

Several committee Democrats, including California Sen. Dianne Feinstein, called Tuesday for stronger rules for companies to seek American workers first before importing H-1B immigrants.

Norman Matloff, a professor of computer science at UC Davis and longtime critic of H-1B visas on grounds they depress wages and employment for U.S. tech workers, called the green-card provisions "the scary part," because they are virtually unlimited and would not necessarily attract only the "best and brightest."

Foreign graduate students would have to have a job offer, "but it could be a clerk at Radio Shack," Matloff said.

Falling wages

Skilled foreign workers would no longer be locked in to their job at one employer under the bill, an aspect Matloff praised. But with a potential flood of new workers in the so-called STEM fields, he argued that wages in those fields would fall, hurting workers and creating a "terrible disincentive" for young Americans who might want to study science, technology, engineering or math.

He said the covered fields could be quite broad.

"You're talking about people in zoology, you're talking about people in quasi-STEM things, of which there are many," Matloff said. "When you add up all those people, it's a ton of people."

A tech industry lobbyist who did not want to be identified said there is a shortage of U.S. workers with advanced degrees in the science and math fields, and that the provision won't entice a flood of immigrants because requiring a master's degree or Ph.D. results in "a very narrow category of people."

No cap, no standards

A bill by Rep. Lamar Smith, R-Texas, that passed the House last year but died in the Senate had a similar provision on green cards for foreign graduate students in the STEM fields, but it would have capped the number at 55,000, and removed those slots from another visa category. The current Senate bill has no cap.

A report by the National Science Foundation, a quasi-government body, said that in 2009, 168,900 foreign students were enrolled in science and engineering graduate programs. But if a chance at permanent U.S. residency is attached to such degrees, that number could swell, Hira said. Most of them would come from master's programs, he said, because Ph.D.s take too long to earn to draw a large number of students and are not as lucrative for universities.

Hira predicted that the provision would "increase wage competition, and there's a good chance of crowding out American students from those fields, too."

The House wrestled with how to set quality standards on the degrees by limiting the green cards to certain high-quality research universities, but without setting the exact criteria. The Senate bill sets no standards.

'Conflict of interest'

"The universities can make money off this, so you're basically putting them in charge as the gatekeepers for selling green cards," Hira said. "It creates conflict of interest."

The Senate Judiciary Committee will continue to work next week on the overall bill, which was conceived by the bipartisan "Gang of Eight" group of senators. Those lawmakers are seeking the support of Utah Republican Orrin Hatch, who wants more H-1B visas and less-strict rules requiring companies to show they sought American workers.

Carolyn Lochhead is The San Francisco Chronicle's Washington correspondent. E-mail: clochhead@sfchronicle.com