A surprise appearance by Apple Inc Chief Executive Steve Jobs at the company's annual developer conference could boost its stock on Monday, but his absence might trigger a bigger move in the other direction.

The Wall Street Journal kicked off speculation of an early return by the ailing Jobs, who had said he would be out until the end of June. Blogs and other media jumped on the report that the CEO could appear at Apple's Worldwide Developer Conference in San Francisco on Monday.

Jobs, 54, the quintessential man in black, founded Apple, rescued it from mediocrity in the late 1990s, launched the iPod and the iPhone and is seen as its heart and soul.

Canaccord Adams analyst Peter Misek sees a rally of 1 to 5 percent in Apple's stock if Jobs makes an appearance, but no downside if he doesn't.

Global Equities Research senior analyst Trip Chowdhry said Apple's stock will likely remain high if Jobs appears, but could sell off as much as 10 percent if he doesn't, a scenario he finds more likely.

But the company's strong performance while Jobs has been recuperating indicates he is no longer crucial to the company's success, Broadpoint AmTech analyst Brian Marshall said.

Stock in the Cupertino-based company closed at $144.67, about 85 percent ahead of January's 52-week low of $78.20. But it was up less than 1 percent on Friday after news that Jobs might return early.

It's not just about Steve Jobs, Marshall said. Investors are very comfortable with Chief Operating Officer Tim Cook as Apple's next CEO, he added.

BMO Capital Markets analyst Keith Bachman said a Jobs cameo would strengthen Apple shares, but less than in the past.

If he made a cameo appearance on Monday and the wind didn't blow right through him, the stock would go up, he said, but the size of the rally would depend on other factors such as announcements regarding Apple's iPhone.

Apple's stock is historically volatile during the company's June developer conference. It dropped about 7 percent over the course of the conference in 2008 and about 4 percent in 2007.

If this had happened one or two years before, the stock would have (had) huge volatility. But I think investors are conditioned to the fact that Steve's health is a variable that needs to be dealt with on an ongoing basis, Bachman said.

Apple managers are trying to coordinate Jobs' return with a product launch or public event, the Journal reported, but cited sources that Jobs is one real sick guy.

AllThingsD, a website dedicated to news, analysis and opinion about the digital revolution, speculated that Jobs, who is known for ending presentations with one more thing, might himself be the surprise at the Monday keynote.

Wired.com reported that such a Jobs' appearance would be dramatic and a crowd pleaser, but Gawker cautioned that Apple might not want a sickly leader on stage.

The CEO is notoriously headstrong about these sorts of things. If he wants to show up on Monday, he will, Gawker said.

(Reporting by Clare Baldwin in San Francisco; Editing by Peter Henderson, Leslie Gevirtz, Richard Chang)

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