UPDATE 2-Greece's NBG takes H1 hit from bond swap writedown

* NBG writedowns on Greek govt bonds pretax 1.645 bln euros

* H1 profit falls 80 pct y/y pre-PSI bond writedown

* Provisions up 27 pct y/y to 822 mln euros

(Adds deputy CEO comment, details)

By George Georgiopoulos

ATHENS, Aug 30 (Reuters) - National Bank of Greece (NBGr.AT), the country's largest, made a big first-half loss on government debt writedowns and said it would not rush into big strategic moves, even as local rivals seek security in mergers.

Troubled by sovereign debt downgrades, deposit outflows and rising loan losses in a deepening recession, Greek banks are exploring tie-ups to bolster their financial strength in a bid to regain access to wholesale funding markets.

NBG (NBGr.AT) lost 1.31 billion euros ($1.9 billion) from its planned participation in a voluntary swap (PSI) of Greek government bonds, aimed at relieving the country's debt burden.

Excluding this provision, net first-half earnings would have reached 29 million euros, down 80 percent year-on-year, NBG said, well below market expectations; analysts polled by Reuters had forecast on average pre-PSI net profit of 126.3 million euros.

CEO Apostolos Tamvakakis said NBG would decide on its next strategic moves once there is more clarity on the outcome of the debt exchange plan and a diagnostic test of Greek banks' loan books by BlackRock Solutions, commissioned by the central bank.

NBG tried to take over peer Alpha Bank (ACBr.AT) earlier in the year, but its offer was turned down. Alpha on Monday decided to merge with EFG Eurobank (EFGr.AT) instead via a share swap to form the largest lender in southeast Europe.

"NBG has consistently promoted the idea of consolidation to strengthen the sector. The Alpha-EFG proposed plan is a move in the right direction," Deputy CEO Anthimos Thomopoulos told analysts on a conference call.

He said the deal also created opportunities for NBG, as peers focus on putting together their challenging merger plan.

NBG said Turkish subsidiary Finansbank contributed 235 million euros in net profit in the first half, helping to offset adverse conditions in the group's home market.

Thomopoulos said NBG was in no rush to sell a stake in Finansbank and would wait for the right market conditions.

Despite the impact of a 1.339 billion euro after-tax writedown on the bond rollover plan expected to take place in October, NBG said its Core Tier 1 ratio was over 10 percent at the end of June, one of the highest in Europe's banking sector.

With conditions at home severely stressed by a long and deep recession, provisions for bad and doubtful loans rose 27 percent year-on-year to 822 million euros, with executives forecasting a couple of more quarters of provisions at a similar level. (Additional reporting by Lefteris Papadimas; Editing by Will Waterman)