By Pavel Polityuk

YALTA, Ukraine (Reuters) - Senior European Union officials pressed Ukrainian leader Viktor Yanukovich on Friday to release jailed opponent Yulia Tymoshenko before a landmark summit, but he said he had not taken a firm decision on her case.

Yanukovich, speaking at a gathering of European leaders and officials in Crimea, said his ex-Soviet republic was committed to signing key agreements with the EU at a November summit, marking Ukraine's pivotal shift towards integration with Europe.

But, replying to questions from Ukrainian opposition leaders over whether he would release former prime minister Tymoshenko, he said only that he was trying to find a way of approaching this "difficult question".

Tymoshenko, Yanukovich's most formidable political rival, was jailed for abuse of office in 2011 after a trial which the EU has said smacked of selective justice.

European envoys have been pressing him to pardon her so she can go to Germany to get treatment for back trouble which has kept her confined in hospital under prison guard.

But he said: "At the moment, we have not yet said either 'Yes' or 'No' (to her being released)", adding there was still time to work out a compromise.

Lithuanian President Dalia Grybauskaite, whose country holds the rotating EU presidency, said Ukraine would have to meet three criteria, including freeing Tymoshenko, for deals on association and free trade to be agreed at the summit in Vilnius, Lithuania.

"Without these, there will be no signing. There must be no illusions that just a little bit can be done or something be done only in a first reading in parliament," she told journalists.

"The request from the European Union on Tymoshenko's case is still on the table and, without a solution, I do not see a possibility for the signature," she said.

Her strong words were backed up by an EU group, which included Swedish Foreign Minister Carl Bildt and met Yanukovich separately.

In a statement, they said they had underlined the importance of Ukraine meeting its obligations, including over Tymoshenko, stressing "time is getting short".

If Tymoshenko was released and became politically active again, she could threaten prospects of Yanukovich's election for a second term in 2015.

Answering questions from her political allies during a panel discussion, Yanukovich said: "We are trying, and are seeking even today, to find a way of approaching this very difficult question relating to Tymoshenko." But he said no firm decision had been reached.

POSSIBILITY OF A PARDON

Asked if he would sign a pardon, Yanukovich appeared to suggest Tymoshenko would first have to acknowledge her guilt.

"Nobody has a bigger interest in solving this issue than I. But there are obstacles. An answer has to be given to ... the courts. Only the court can give an answer or (there can be) a voluntary decision by Tymoshenko. The answer lies in finding a compromise with the participation of Tymoshenko," he said.

The agreements on political association and free trade which Ukraine, to the dismay of its former Soviet master Russia, is hoping to sign with the EU will require the backing and subsequent ratification of all 28 member states.

Yanukovich has come under strong pressure from Moscow to give up its drive towards integration with mainstream Europe and instead join a Russian-led Customs Union with promises of cheaper gas and softer duties on goods.

Yanukovich won expressions of support from EU officials for withstanding this pressure and sticking to his course of Euro-integration.

(Writing By Richard Balmforth; Editing by Andrew Heavens)