Samsung slashes Q3 profit estimate by a third after pulling plug on Note 7

* Samsung lowers Q3 profit guidance by third to 5.2 trln won

* Samsung shares touch 1-month low on earnings worries

* Firm scrapped sales, output of flagship Note 7 smartphone

* Crisis could seriously damage Samsung long-term -analysts

* Investors raise prospect of share buyback to soothe nerves (Adds investor comment on Q4 impact, share buyback prospects)

By Se Young Lee

SEOUL, Oct 12 (Reuters) - Samsung Electronics Co slashed its quarterly profit estimate by a third on Wednesday, soaking up a $2.3 billion hit from ditching its flagship smartphone in what could be one of the costliest product safety failures in tech history.

Quantifying the financial pain of Tuesday's move to scrap the Galaxy Note 7 smartphone after a global recall and weeks of mounting problems, the world's top smartphone maker said it expects its July-September operating profit was 5.2 trillion won ($4.7 billion), down from the 7.8 trillion won it estimated five days ago.

Samsung said in a statement the 2.6 trillion won ($2.3 billion) guidance cut reflects the sales and earning impact it currently expects from the decision to permanently halt sales of the $882 Note 7 device. Its third-quarter revenue estimate was also cut to 47 trillion won from 49 trillion won previously.

The new earnings guidance is 30 percent below third-quarter 2015's operating profit, and left investors and analysts pondering the longer impact on Samsung's brand and earnings. Rival suppliers of smartphones that use the Android operating system, like Samsung's, stand to benefit if the Note 7 damage drive consumers elsewhere.

"It's possible there could be additional profit impact in the fourth quarter but it likely won't be as large as the third quarter," said Park Jung-hoon, a fund manager at HDC Asset Management, which owns shares in Samsung. "I think it's possible for fourth-quarter profits to come in as much as the high 7 trillion won range."

Samsung shares ended down 0.7 percent on Wednesday, with the Seoul market closing before the earnings guidance cut was announced.

HDC's Park said the initial guidance issued last week likely already factored in a 1 trillion won profit impact, putting the total third-quarter earnings hit at around 3.6 trillion won. While this was a major blow, he said some investors had feared the profit impact could be as large as 5 trillion won this year.

BILLION-DOLLAR BUYBACK?

Samsung shares have already fallen 10 percent this week and are on track for their biggest weekly decline since May 2012, having touched a one-month low of 1.494 million won as investors worried the Note 7 crisis could inflict long-term damage on Samsung's reputation and earnings.