TALLINN (Reuters) - Estonia's president has nominated Juri Ratas, the new leader of a center-left, traditionally pro-Russian party, as prime minister who promised to leave foreign policy unchanged in a region worried about possible Russian aggression.

Concerns in the Baltics and wider Eastern Europe about Russian expansionist ambitions have become more acute since Donald Trump's U.S. election victory because of his stance on NATO. The region sees the alliance as their main protection against Russia, but Trump has made pledges that would undermine NATO.

Ratas took over as chairman of the Centre Party this month after its aging founder stepped aside. Under Edgar Savisaar, the party did not criticize the foreign policies of Russian President Vladimir Putin and had a cooperation agreement with his party. However, its stance was not anti-EU or anti-NATO, and was less close to Moscow than counterparts in Moldova or Bulgaria.

"I am confident that Juri Ratas will be able to form a strong and willing to act government. Estonia’s current direction in foreign and security policy should remain and the leaders of all three parties have confirmed this to me," President Kersti Kaljulaid said in a statement.

On Saturday the three parties aiming to form the new coalition government agreed to keep to the same security and foreign policies of the previous government, including support for sanctions imposed on Russia and keeping NATO defense spending at two percent of GDP or greater.

Fears were stoked by Trump's remarks in July to the New York Times that he would consider a country's contribution to the alliance first before coming to a country's defense.

A new ruling coalition under Ratas has the support of at least two junior partners to hold a total of 56 seats in the 101 seat parliament.

Estonia, Latvia and Lithuania are members of the EU, Euro zone and depend on their NATO allies to police their airspace, and are expecting NATO alliance members to deploy ground troops next year to boost their defense forces and to deter Russia.

The Centre Party also drew support from Estonia's ethnic Russians, who make up a quarter of its 1.3 million inhabitants. Its framework cooperation agreement with Putin's United Russia party was intended to bolster that support base but in a recent interview, Ratas has played down the agreement, saying it had been unused for several years. However he has not repudiated the agreement despite intense political pressure to do so.

Outgoing Prime Minister Taavi Roivas lost a parliamentary vote on confidence this month after his junior coalition partners deserted his Reform Party-led government amid after internal squabbling.

(Reporting by David Mardiste; Editing by Johan Ahlander and Raissa Kasolowsky)