Google's success has already spurred Microsoft to develop its own Internet search engine (a project code-named Underdog), but Google has legions of engineers banging away on a range of projects of its own that, if successful, could dislodge Microsoft from the pre-eminent spot it has enjoyed since the early 1980's.

Of course, Silicon Valley has had past pretenders to the throne. Netscape, which went public 10 years ago this month, and its Web browser, Navigator, were supposed to fell Microsoft -- but it is Netscape that is no longer in business. And while Google is riding high, those closely following the company caution that it is hardly invincible; an inflated stock price, a desire to compete in too many sectors simultaneously or simple hubris might cause it to stumble, they say. Even Microsoft, after all, has had legal troubles.

Still, similarities between Google and Microsoft are evident to local entrepreneurs including Steven I. Lurie, who worked at Microsoft between 1993 and 1999 but now lives in San Francisco, and Joe Kraus, a founder of the 1990's search firm Excite.

"There's that same 'think big' attitude about markets and opportunities," said Mr. Lurie, who has visited the Google campus in Mountain View many times to see friends who work there. "Maybe you can call it arrogance, but there's that same sense that they can do anything and get into any area and dominate."

To place Google in context, Mr. Kraus offered a brief history lesson. In the 1990's, he said, I.B.M. was widely perceived in Silicon Valley as a "gentle giant" that was easy to partner with while Microsoft was perceived as an "extraordinarily fearsome, competitive company wanting to be in as many businesses as possible and with the engineering talent capable of implementing effectively anything."

Now, in the view of Mr. Kraus, "Microsoft is becoming I.B.M. and Google is becoming Microsoft." Mr. Kraus is the chief executive and a founder of JotSpot, a Silicon Valley start-up hoping to sell blogging and other self-publishing tools to corporations.

Just as Microsoft has been seen over the years as an aggressive, deep-pocketed competitor for talent, Internet start-ups in Silicon Valley complain that virtually every time they try to recruit a well-regarded computer programmer, that person is already contemplating an offer from Google.