* Investors seek more info on Jobs' medical leave
* Quarterly sales expected to surge 50 pct over year ago
* iPhone, iPad to show strong holiday shopping season
* Wall Street sees earnings of $5.40/shr, sales at $24.4 bln
By Gabriel Madway
SAN FRANCISCO, Jan 18 (Reuters) - Apple Inc is set to report a stunning 50 percent jump in quarterly sales on Tuesday, as its iPhone and iPad excited holiday shoppers, but the consumer electronics powerhouse may face more pressing questions about the health of iconic chief executive Steve Jobs.
The world's most valuable technology company announced on Monday that Jobs would take a medical leave of absence without specifying a return date or detailing Jobs' condition, leaving investors in an information vacuum.
The surprise announcement -- made on a U.S. market holiday -- dragged Apple shares down more than 6 percent in European trading. They are up 62 percent in the past 12 months on the Nasdaq stock exchange.
"Steve Jobs is seen by the market to be a major force in Apple's strategic direction," said Richard Windsor, global technology specialist at Nomura. "If his pancreatic cancer has returned, one could be quite worried."
Jobs' latest leave comes nearly two years after he took a six-month break to undergo a liver transplant. He also took time off after pancreatic surgery in 2004.
Apple has not dwelt on Jobs' health, and Jobs himself asked for respect for his privacy in a memo to employees made public on Monday.
In Jobs' absence, it will be up to chief operating officer Tim Cook to decide how much to tell investors about the absent chief executive, and what Apple plans to do with its $50 billion-plus pile of cash and investments.
Less of a showman than Jobs, the 50-year old Alabama native is not expected to make any grand pronouncements. But he is regarded as a safe pair of hands for the company, having stood in for Jobs successfully twice before.
In Asia, tech shares gained, helped by hopes of a recovery in chip prices and expectations that nimble firms may slow the runaway success of Apple after the news that Jobs would take medical leave.
Still, analysts said the impact on Apple's operations and its Asian rivals and partners should be limited in the short-term given a strong product line-up.
"Apple's roadmap is all set and its iPhone 5 is ready to go, leaving little room for competitors to cut into its share," said Bonnie Chang, an analyst at Yuanta Securities in Taipei.
HUGE HOLIDAY SEASON
Aside from Jobs' health, the company is entering 2011 on a roll, a cash-generating machine with surging sales across its product lines, even as it confronts rivals determined to halt its stunning run of success.
Wall Street is expecting Apple's quarterly revenue to swell more than 50 percent to more than $24 billion after a bumper holiday shopping season. That would be a sparkling performance for a company of any size, much less one with a market value above $300 billion.
Apple's advantages are well-documented: the global spread of the iPhone, which is expected to sell more than 60 million units this year; the rise of the iPad, which single-handedly created the tablet computing market; and continued strong growth from the resurgent Mac line of computers.
Wall Street's benchmarks for Apple's fiscal first quarter, which includes the holiday shopping season, are sales of roughly 15.5 million iPhones, 5.5 million iPads and 4 million Mac computers.
After the close of regular trading hours on Tuesday, Apple is expected to report earnings of $5.40 a share on revenue of $24.4 billion, according to Thomson Reuters I/B/E/S.
According to StarMine's SmartEstimate, which places more weight on recent forecasts by top-rated analysts, Apple should post EPS of $5.47 on revenue of $24.5 billion.
Even so, an out-sized surprise in Apple results has become an article of faith among investors. The company has beaten Wall Street's estimate by an average of 29 percent over the past two years, and bested on revenue by 9 percent on average.
"The only surprise in earnings is if there is anything less than glorious news," said Barry Jaruzelski, a partner at consulting firm Booz & Co, last week.