The total jobs Asians hold in tech workplaces are almost evenly split between Asian-American citizens and non-citizen Asians, according to an analysis of the latest Census Bureau data by this newspaper.

Census Bureau data for 2010 released in late November shows that just more than half of all Bay Area tech jobs were held by Asian workers and their double-digit employment gains since 2000 came from jobs lost among white tech workers.

An analysis of the Census data shows that among tech jobs held by Asians across the Bay Area, 25.5 percent belonged to citizen Asians — as the Census Bureau classifies them — with non-citizen Asians holding 24.6 percent of the jobs.

The data helps underscore some of the rising tensions in tech workplaces around the Bay Area as white workers are displaced by both citizen- and non-citizen Asians, who are often allowed to work in the United States through H1-B visas that give preference to workers with tech skills.

But Silicon Valley always has relied on a fresh supply of “new brains,” no matter where they come from, said Leslie Berlin, historian for the Silicon Valley Archives at Stanford University.

“When you have a system that’s dependent on intellectual fire power, getting this constant refresh of new young brains is a requirement to move forward,” Berlin said. “In the beginning it was more or less of a domestic type immigration, where people were coming in from other parts of the U.S. to the west. If you’re looking directly at what is best for Silicon Valley, on the level of productivity and innovation, it’s in the region’s best interest to be able to pull from the widest and deepest pool possible.”

Buck Gee, 63, retired in 2008 as the vice president and general manager of Cisco Systems (CSCO)’ datacenter business unit and worries about a possible backlash against Asians as they fill more tech jobs.

Gee, president of the board of the Angel Island Immigration Station Foundation, which works to preserve the historic immigration center, sees similarities in the current debate in Congress over the future of H1-B visas aimed at non-citizen tech workers and anti-immigrant sentiments that go back to the first Chinese and Japanese immigrants who arrived in California in the late 1800s and early 1900s.

“After the Chinese helped build the railroads, by the 1880s there was a recession and white workers in San Francisco and California were complaining that the new immigrants were taking their jobs,” Gee said. “Now we’re seeing a repeat of what happens when the new immigrants come in and compete. And there’s a backlash. I don’t like it. But it’s common.”

While the overall 2010 Census showed an almost even divide in Bay Area tech jobs, non-citizen Asians dominated several categories, such as software developers.

In Santa Clara County, for instance, non-citizen Asians held slightly more than 35 percent of the software developer jobs compared to citizen Asians, who represented slightly more than 26 percent of those positions. In San Mateo County, non-citizen Asians held almost 33 percent of the software developer jobs compared to 27 percent of citizen Asians.

Citizen Asians tended to dominate — with larger disparities — jobs such as computer programmers, computer support specialists and database administrators.

In Santa Clara County, citizen Asians held 32 percent of the computer programmer jobs while non-citizen Asians held 18 percent. In Alameda County, citizen Asians had 25 percent of the computer programmer jobs compared to 12.5 percent of non-citizen Asians.

The Census did not differentiate between citizen and non-citizen Asian employment in 2000, so it’s impossible to compare gains by either group for 2010.

The latest data comes out amid an on-going debate in Congress over increasing pressure to reform U.S. immigration policy, a key issue for Silicon Valley technology companies that have come to rely on foreign-born labor.

Last week the House passed the STEM Jobs Act, which eliminates the “diversity lottery green card program” and allocates 55,000 new green cards to qualified foreign graduates of U.S. universities with advanced degrees in science, technology, engineering and math.

For non-citizen engineering students at UC-Berkeley, the debate in Washington leaves them wondering about their futures in the Bay Area’s tech industry, said Associate Dean Oscar Dubon, who is in charge of “equity and inclusion” for UC-Berkeley’s college of engineering.

“Seniors are wondering what they’re going to do when they graduate,” Dubon said. “And international students are certainly feeling that.”

Mercury News Library Director Leigh Poitinger contributed to this story. Contact Dan Nakaso at 408-271-3648. Follow him at Twitter.com/dannakaso.