WARSAW, Sept 2 (Reuters) - Poland's Supreme Court will seek help from the European Union's top court to resolve a standoff over judicial appointments that are blocking proceedings in a long-running case on foreign currency loan disputes, a spokesman said on Thursday.

He was speaking after the court failed again to issue a decision on how lower courts should treat the cases involving thousands of Poles who took out mortgages in Swiss francs more than a decade ago to take advantage of low Swiss interest rates, only to face higher costs when the value of the zloty slumped.

"The sitting of the Supreme Court ended with a decision to refer preliminary questions to the Court of Justice of the European Union (CJEU)," court spokesman Aleksander Stepkowski said.

"Under the decision the burden remains with the common courts, who did not receive the support of the Supreme Court."

Before the sitting, lawyers had said that a conflict between old and newly-appointed judges made a decision unlikely.

Many old judges in the Supreme Court believe that new judges were appointed illegally as a result of reforms by the ruling Law and Justice (PiS) party, which critics say have politicised the judicial system.

Some old judges say verdicts reached with the participation of new judges could be questioned in future. The Supreme Court decided to send three questions on this issue to the CJEU, Stepkowski said.

"Of course, the system for appointing judges is very important, but 700,000 people are waiting for this case, they could have chosen another case to ask these questions," said Andrzej Zorski, a lawyer specialising in Swiss franc mortgage cases.

The court, sitting with all the judges of the Civil Chamber, had been due to issue the guidance in May, but postponed a decision to ask for opinions from institutions including the central bank, financial regulator KNF and the children's rights ombudsman.

Warsaw's WIG Bank's index was up 0.4% following the verdict.

($1 = 3.8107 zloty) (Reporting by Alan Charlish and Pawel Florkiewicz Editing by Robert Birsel and Emelia Sithole-Matarise)