BANGKOK, Jan 14 (Reuters) - Oman have sacked Argentine coach Gabriel Calderon and replaced him with Uruguayan Julio Cesar Ribas just three weeks before the third round of World Cup qualifiers begin.

The newly-elected board of Oman's soccer federation opted to ditch Calderon after 21 months in charge and bring in 50-year-old Ribas, a former coach of Uruguayan side Penarol and Italian Serie B side Venezia.

"Mr. Calderon has left, we have a new coach, he will coach the team for the World Cup qualifiers and next year's Gulf Cup," an Oman Football federation official told Reuters by telephone on Monday.

Calderon, 47, a former Saudi Arabia coach and losing finalist with Argentina in the 1990 World Cup, failed to make an impact with the national team.

They finished bottom of their group at the Asian Cup and have won only one of their four World Cup warm-up matches.

Ribas made over 400 league appearances in Uruguay and was capped 15 times by his country, for which his son Sebastian is a player. The Oman job is Ribas's first in the Gulf.

Oman have been drawn in Group Two of Asian qualifiers for the 2010 World Cup, alongside Japan, Thailand and Bahrain. (Reporting by Martin Petty; Editing by Peter Rutherford)