Westinghouse Electric Co. has hired 4,000 people in the past four years, many of them engineers and project managers needed to help build nuclear power plants at home and abroad.

If the nation is experiencing a shortage of workers in the "STEM" fields of science, technology, engineering and math, Westinghouse hasn't seen it.

"We haven't had a problem," company spokeswoman Vaughn Gilbert said.

But other companies, business groups and policy-makers long have been concerned about the capacity of the nation's STEM workforce.

Is the nation graduating enough scientists and engineers to fuel the nation's economic and security needs?

There is no laboratory-tested answer.

STEM work force capacity varies by region and scientific field. Talent depth varies according to the experience and education levels that employers demand at any given time.

There is a Darwinian component, too, with some companies proving more adept at identifying and snagging talent.

"I think the data are unclear as to how large the STEM demand is and where there are acute shortages and where there aren't," said U.S. Rep. David Wu, D-Ore., chairman of the House Subcommittee on Technology and Innovation, which has held hearings on STEM issues, including work force capacity.

Mr. Wu does see an acute shortage in at least one area -- information-technology workers for the health care sector. He sponsored a bill -- now folded into the economic stimulus package -- to provide federal money to train 10,000 health care IT workers by 2010.

To Mr. Wu, the issue is broader than a debate over numbers of STEM workers. He said schools must strive to make all students scientifically literate so they can be good citizens and jump into a STEM field at any number of points in their educational journeys.

Some differ in what they count as STEM fields. The National Science Foundation includes the social sciences, such as psychology and economics, but a consortium of business groups focused more narrowly on math, computer science, natural sciences and other sciences.

In a 2005 report called "Tapping America's Potential: The Education for Innovation Initiative," the business consortium called for doubling, to 400,000, the number of U.S. college students annually graduating with bachelor's degrees in STEM fields. The groups wanted the target reached by 2015, warning that a diminishing STEM work force could yield a Sputnik-style period of foreign technological superiority.

The group cited declining numbers of U.S. engineering students, what it called overreliance on foreign scientists by U.S. companies and increasing numbers of STEM graduates in China, South Korea and other countries. It called for improvements in U.S. public-school science courses and incentives for students to major in STEM fields at the college level.

The alarm was sounded again as recently as September, when a Bayer Corp. survey of Fortune 1,000 executives revealed concerns about the nation's STEM capacity.

The survey included 100 executives at STEM-related companies. Ninety-five said they were concerned about the nation losing its economic competitiveness because of a shortage of STEM talent; 55 reported shortages at their own companies, and 68 expressed concern about other countries' growing access to STEM talent.

"We do see a demand issue, and we have real concerns," said Rebecca Lucore, executive director of the Bayer USA Foundation, which sponsors education and workforce development initiatives involving schools, universities and community groups.

The executives called for additional efforts to recruit women and underrepresented minorities into STEM professions.

Bill Gates is among those concerned about the talent pool. Without using statistics, he told a House committee last year that American companies "face a severe shortfall of scientists and engineers with expertise to develop the next generation of breakthroughs."

Brian Kennedy, vice president for government and external relations for the Pittsburgh Technology Council, a business group with about 1,400 members, said the metropolitan area isn't producing enough STEM workers to meet local needs.

In a recent survey, members ranked the attraction of experienced talent their No. 2 concern, behind only business development. Other top concerns included talent retention and attraction of entry-level talent, Mark Whittaker, strategic analyst for the council, said.

From 2004 through last year, members posted 34,700 job openings on the council's Web site, including 18,430 openings for computer scientists, 2,650 for computer engineers and 950 for electrical engineers.

One person's shortages are another's mirage.

While calling for additional study, Rand Corp. in a report five years ago said it found no evidence of current or looming shortages of STEM talent at various federal agencies.

Rather, in many fields, Rand said, the supply of workers appeared to exceed demand.

Michael Teitelbaum, vice president of the New York-based Sloan Foundation, a philanthropy focused on STEM and economic issues, told Mr. Wu's subcommittee two years ago that there might be isolated shortages in certain fields.

But he said the notion of widespread shortages was invented by "interest groups and their lobbyists," including employers who want to increase labor pools and keep labor costs down; universities seeking an influx of grant money and graduate students; and others who see STEM advocacy as a way to attract funding.

According to the U.S. Department of Labor's "Occupational Outlook Handbook," future demand for STEM workers will vary considerably by field.

From 2006 through 2016, demand for mechanical engineers, for example, is projected to grow by 4 percent; environmental scientists and hydrologists, 25 percent; and software engineers 38 percent.

Sometimes, the data disagree or projections are at odds with anecdotal evidence about STEM demand.

The U.S. Labor Department projects a 7 percent spike in demand for nuclear engineers from 2006 through 2016, a rate it considers about average.

Yet Mr. Gilbert, the Westinghouse spokesman, described the nuclear field as "hot," not only for engineers but the skilled tradesmen needed to build power plants.

Depending on the number of new facilities brought on line in coming years, a panel of the American Physical Sociey last summer said the need for nuclear engineers at power plans could jump about 60 percent, to 12,500, by 2020. The society is a professional group of physicists.

Companies with a continuing need for new talent have established a recruiting infrastructure to give them a leg up on competitors.

Mr. Gilbert said Westinghouse has partnerships with engineering programs at various universities.

Software engineering giant Ansys Inc. has a two-person in-house recruiting staff to scour resumes, work the phones and raise the company's profile among candidates for technical and non-technical positions. Employees get $3,000 bonuses for steering new hires to the company. And at any given time, the Cecil-based company is working with two dozen or more university engineering students through a co-op program that often leads to job offers.

The recent economic downtown has added another dimension to the debate, but Renee Starek, assistant director of the career center and a career consultant at Carnegie Mellon University's Mellon College of Science, said the job prospects of Carnegie Mellon graduates with STEM degrees so far don't seem affected.

Carnegie Mellon senior Brian Krausz, 20, a Long Island native majoring in computer science and minoring in software engineering, said he had four job offers and declined second interviews with four other companies.

After graduating in May, he's moving to Boston to take a software engineering position on the "new initiatives team" at TripAdvisor, the online travel agency.

He said "companies that have the money to burn through this" slowdown are still hiring and recalled getting this message from TripAdvisor:

"We're still looking for two more software engineers. Do you know anyone?"

INSIDE: STEM, an education planning guide, features the fields of science, technology, engineering and mathematics.