SEOUL, Jan 29 (Reuters) - Hyundai Motor on Thursday reported a 40% fall in fourth-quarter operating profit versus a year earlier, missing analysts' estimates by a big margin, as U.S. tariffs offset the positive impact of a weaker South Korean currency.

This marks the third consecutive decline in quarterly profit for the South Korean automaker, as the U.S. administration slapped 25% tariffs on autos in April which were slashed to 15% in November after a trade deal with Seoul.

U.S. President Donald Trump said on Tuesday he would hike tariffs on autos and other imports from South Korea, blaming a delay in enacting the trade deal agreed last year that enabled the auto tariff cuts.

Hyundai, which together with affiliate Kia is the world's third-biggest automaking group by sales, booked operating profit of 1.7 trillion won ($1.19 billion) for October-December, compared with 2.8 trillion won in the same period a year earlier.

The result compared with a 2.7 trillion won LSEG SmartEstimate drawn from 17 analysts. The consensus estimate gives more weight to analysts who are more consistently accurate.

($1 = 1,426.2900 won)

(Reporting by Hyunjoo Jin and Heekyong Yang; Editing by Christopher Cushing)