SAN FRANCISCO  Silicon Valley was abuzz Wednesday with news that the Justice Department had begun an antitrust investigation into the hiring practices of some of the best-known companies in the technology and biotech industries, including Google, Apple, Yahoo and Genentech.

The question being asked most frequently was how the word “anticompetitive” could possibly be applied to the industry’s perpetual fight over talent. But some employment and antitrust lawyers, recruiters and others said that while Valley companies compete aggressively for top engineers, marketers and executives, it is not a free-for-all.

“There is a gentlemen’s understanding all over the Valley that, it’s not that you don’t hire, it’s the process by which you hire,” said Randy Komisar, a partner at the venture capital firm Kleiner Perkins Caufield & Byers.

Some veteran human resources executives said that hiring was not so much the issue; employees are free to look for work pretty much anywhere. But they say major companies often have an unwritten agreement to not actively poach employees from their partners.