* S8 has biggest screen to date for Samsung premium phones
* Samsung also launching new AI assistant Bixby
* Aims to recover market share vs Apple after Note 7 debacle
* Samsung exec says S8 sales to beat S7s
* S8 to go on sale on April 21 (Changes date; adds comments from Samsung executive on sales expectations and analyst's sales projection)
By Se Young Lee and Anjali Athavaley
SEOUL/NEW YORK - March 30 (Reuters) - Samsung Electronics Co Ltd unveiled its Galaxy S8 flagship smartphone as it battles to regain the market leadership it lost to Apple Inc after the embarrassing withdrawal of the fire-prone Note 7s.
Boasting some of the largest wrap-around screens ever made, the long-awaited S8 is the South Korean technology company's first new premium phone after it permanently halted sales of Galaxy Note 7 smartphones in October after a failed recall attempt. The incident cost Samsung $5.5 billion in profit and dealt a heavy blow to its reputation.
Two versions of the Galaxy S8, code-named Dream internally, were launched at a media event in New York on Wednesday, with 6.2-inch (15.75 cm) and 5.8-inch curved screens. They will go on sale on April 21 in three markets - Canada, South Korea and the United States - and roll out to other markets in the following weeks.
"We must be bold enough to step into the unknown and humble enough to learn from our mistakes," Koh Dong-jin, the company's mobile chief, said at the event after acknowledging that it had been a challenging year for Samsung.
Koh expects the S8 to outsell the 2016 predecessor Galaxy S7, which Samsung said last week set the firm's internal record for first-year sales, despite the fact S8 sales will begin more than a month later than the S7's last year.
Researcher Counterpoint says Samsung could sell as many as 53 million S8s this year, which it says compares with fewer than 50 million S7s sold in 2016.
U.S. carriers T-Mobile US Inc and Verizon Communications Inc announced retail pricing for the smaller S8 around $700. The larger phone will sell for $840 at Verizon and $850 at T-Mobile.
The S8 features Samsung's new artificial intelligence service, Bixby, with functions including a voice-commanded assistant system similar to Apple's Siri. There is also a new facial recognition application that lets users unlock their phones by looking at them.
Samsung hopes the design update and the new features, focused on making life easier for consumers, will be enough to revive sales in a year Apple is expected to introduce major changes to its iPhones, including the very curved screens that have become staples of the Galaxy brand.
The S8 is also crucial for Samsung's image as a maker of reliable mobile devices. Analysts say Samsung must prove it can avoid a repeat of the Note 7 crisis.
"The Galaxy S8 is the most important phone for Samsung in a decade and every aspect will be under the microscope following the Note 7 recall," said Ben Wood, a smartphone industry analyst with UK-based CCS Insight. ($1 = 1,113.8200 won) (Additional reporting by Eric Auchard in London; Editing by Richard Chang and Mark Potter)