If the United States really has a critical shortage of scientists and engineers, why didn’t this year’s graduates get showered with lucrative job offers and signing bonuses?

That’s the question that comes to my mind after reading about Barack Obama’s plans to address the “shortage” we keep hearing about from blue-ribbon commissions of scientists and engineers. He wants to pay for the training of 100,000 more engineers and scientists over the next four years, as my colleagues Bill Broad and Cory Dean note in their excellent analysis of the presidential candidates’ plans to encourage technological innovation.

Now, I’m all in favor of American technological innovation, and I’m glad to see Mr. Obama promising to review the export restrictions that have been so damaging to the aerospace industry (and that were promoted by John McCain because of what he called national-security risks). I’m also all in favor of American scientists and engineers, especially the ones in my family. (My father is a chemical engineer; my brother is an electrical engineer.) I’d love to see American corporations and universities frantically competing to offer them the kind of salaries paid to M.B.A.’s and lawyers.

But employers don’t have to throw around that kind of money because there’s no shortage of workers — and they won’t be increasing their offers if the federal government artificially inflates the labor supply with an extra 100,000 graduates. As Daniel S. Greenberg wrote in the Scientist magazine in 2003: “Despite the alarms, no current or impending shortage exists, and never did. Instead, we’re glutted with scientists and engineers in many fields, as numerous job seekers with respectable credentials can attest.”

The only “shortage” is of American-born scientists and engineers. But with so many talented foreigners competing for positions here in schools and laboratories, it’s entirely rational for American students to head into fields where their skills are in more demand — and harder to replace with foreign labor. Mr. Greenberg sums up their options nicely:

Consider the economic fates of two bright college graduates, Jane and Jill, both 22. Jane excels at a top law school, and after graduation three years later, is wooed and hired by a top law firm at the going rate–$125,000 a year, with a year-end bonus of $25,000 to $50,000. Jill heads down the long trail to a PhD in physics, and after six Spartan years on graduate stipends rising to $20,000 a year, finally gets her degree. Tenure-track jobs appropriate to her rigorous training are scarce, but, more fortunate than her other classmates, she lands a good postdoc appointment–at $35,000 year, without health insurance or professional independence. Three years later, when attorney Jane is raking in $150,000 a year, plus bonuses, Jill is nail-biting over another postdoc appointment, with an unusually ample postdoc recompense of $45,000 per annum. Medicine and business management similarly trump science in earning power.

So why do we keep hearing complaints about a shortage? One recent reason is that it’s been harder for foreign scientists and engineers to get visas since the Sept. 11 attacks. But the quickest and cheapest way to deal with that problem is to increase the number of visas (as Mr. Obama has promised to do).

But even if the visa restrictions are eased, the complaints about a shortage are sure to continue — they’ve been sounded for decades. Why? Well, consider who does some of the loudest complaining: administrators of university science and engineering department that stand to get more funds, and corporate executives hoping to have more future workers trained at taxpayer expense.

The blue-ribbon commissions have kept warning that America’s future is in jeopardy if we don’t train more native-born scientists and engineers, but I don’t see how Americans are worse off by letting some technologies be developed and manufactured by foreigners who can do it more efficiently. Politicians inveigh against the trade deficit in advanced-technology products, but what’s the harm in buying computer disk drives and semiconductor chips produced more cheaply in Asian factories?

And as long as American universities and laboratories keep attracting the world’s best talent, why should we worry about losing our technological edge?