* France faced pressure to call off warships deal
* Decision comes on eve of Ukraine-focused NATO summit
* Russia says cancelling contract no "tragedy" (Adds reactions, details)
By Leigh Thomas
PARIS, Sept 3 (Reuters) - The French government cannot go ahead for now with the planned delivery of a first of two helicopter carriers to Russia, the president's office said on Wednesday, citing Moscow's actions in eastern Ukraine.
France, due to join NATO partners at a summit in Britain from Thursday, has faced fierce pressure from Washington and other allies to halt the sale of the Mistral-class warships, the first of which had been due for delivery in October.
Four hundred Russian sailors have been receiving training to operate the carrier since the end of June at shipyards at Saint-Naizaire, on France's Atlantic coast.
Warning Moscow it could face more sanctions, President Francois Hollande's said last week it would be "intolerable and unacceptable" if it were proven that Russian forces had entered Ukrainian territory, something Russia denies.
"Russia's recent actions run against the foundations of security in Europe," Hollande's office said in a statement after a meeting between the president and his top military advisers.
"The president of the republic has concluded that despite the prospect of ceasefire, which has yet to be confirmed and put in place, the conditions under which France could authorise the delivery of the first helicopter carrier are not in place."
Russian President Vladimir Putin outlined a plan for a ceasefire in eastern Ukraine on Wednesday but the Ukrainian prime minister accused him of trying to deceive NATO and head off new European Union sanctions.
Russia's Defence Ministry played down the French decision, saying it would not hinder the modernisation of its military nor hold back its reform plans, Itar-Tass news agency reported.
"Although of course it is unpleasant and adds to certain tensions in relations with our French partners, the cancelling of this contracts will not be a tragedy for our modernisation (of the army)," Deputy Defence Minister Yuri Borisov told the Russian news agency.
France's decision is likely to take the heat off France when NATO leaders meet in Wales for a summit largely focused on the conflict in Ukraine and growing tensions with Russia.
"Unfortunately Russia has made this kind of decision the only possible decision by its actions," a senior NATO official told journalists in Newport ahead of the summit.
France has until now resisted allies' pressure to halt the delivery of the warships, saying that doing so would hurt Paris more than Moscow.
As recently as July, Hollande said that France would honour the contract for the first carrier, but said he was prepared to review the second due to be delivered in 2016.
And on Tuesday, French diplomats had suggested that the delivery of the first helicopter carrier was likely to go ahead.
Paris has repeatedly said that other countries must share the burden in imposing a new round of sanctions on Russia and that any measures should also include the energy and financial sectors as well as defence.
Signed by then-president Nicolas Sarkozy's conservative government, the 1.2 billion euro ($1.58 billion) contract for two warships was the first by a NATO member country to supply Russia with military equipment.
"Russia used to have a closer partnership with NATO than other countries through the NATO-Russia Council," one high-ranking NATO diplomat said in Newport.
"But this Russia today is no partner." (1 US dollar = 0.7609 euro) (Additional reporting by Adrian Croft and Sabine Sebold in Newport and Alissa de Carbonnel in Moscow; Editing by Alison Williams)