SAN FRANCISCO — Technophiles are eagerly waiting to learn whether the king of digital music can colonize an entirely new category of consumer electronics.

Steve Jobs, chief executive of Apple Computer Inc., is expected to launch at least one revolutionary product today at the Macworld Conference & Expo in San Francisco. Speculation has focused mainly on an Apple-branded cellular phone and a set-top box that allows people to send video from their computers to their televisions.

Although Apple spokeswoman Natalie Kerris declined comment on "rumors and speculation," bloggers, enthusiasts and investors have been continually guessing whether Jobs will unveil a "smart phone" (which some are calling iPhone), iTV or both.

Apple's iPod music player wasn't the first on the market when it launched in 2001. But its sleek design and intuitive user interface quickly made it a hit.

Industry analysts believe another well-designed product from Apple could seriously threaten major tech companies such as Motorola Inc., Nokia Corp., Samsung Electronics Co., Verizon Wireless and TiVo Inc.

Expectations for Macworld are so lofty that a failure to launch an earth-shattering product this week could dent Apple's already volatile stock price, investors say. The stock has traded in a 52-week range of $50.16 to $93.16. It closed yesterday at $85.47 on the Nasdaq Stock Market.

Wall Street's confidence in Apple has wavered slightly because of the possibility improper handling of employee stock options would erase some of Apple's record profits. The scandal threatened to plunge Jobs into a legal morass, if not cost him his job.

Still, anticipation is so breathless in the blog-osphere that some pundits have already credited Apple with changing the global telecommunications sector — even though the iPhone is technically still "vaporware," or nonexistent.

The mere suggestion that Apple might make a glamorous, simple cell phone that downloads, plays and shares digital music has intimidated competitors, said Avi Greengart, an analyst with Current Analysis.

"Even if Apple does not announce a phone, just the threat of Apple's entry could spur innovation," Greengart wrote in a research note Thursday. "If Apple builds a phone that is easy and genuinely pleasurable to use, the company will have a winner no matter how it is priced or sold."

Apple also is expected to unveil a set-top box designed to bridge computers and television sets so users can more easily watch their downloaded movies on a big screen. The move would complement Apple's entry into online movies — it began selling titles through its iTunes store in September.

As Apple launched online movies, Jobs showed off a gadget that streams high-definition videos, selling for $299 starting sometime in the first quarter. Analysts believe the demo was of the prerelease version of the iTV that could be introduced at Macworld, venue for many of Apple's monumental product launches over the years.

The demo, which looked like a flatter but wider version of the Mac Mini computer, worked with computers running Apple's Macintosh or Microsoft Corp.'s Windows systems and used Apple's iTunes software to manage multimedia files. A small hard drive was expected to be included with iTV.

The product could be as revolutionary to digital movies as the iPod was to digital music.