* Initial 25 works to be displayed on "Lost Art" website
* Goal is to help glean tips on provenance of works
* Most of $1.34bln hoard stolen from Jews under Nazi rule (Adds detail from Sueddeutsche on Gurlitt)
By Erik Kirschbaum and Karen Freifeld
BERLIN/NEW YORK, Nov 12 (Reuters) - Germany began publishing an online list on Tuesday of works that were discovered in a huge art stash in a Munich flat last year and believed for the most part to have been stolen or extorted by the Nazis.
The move was welcomed by lawyers representing families whose looted art was feared lost forever. But heavy demand for the government's "Lost Art" website (www.lostart.de) led to technical problems that made it difficult to gain access.
"No one was expecting such a storm of demand," said a spokesman for the Culture Ministry. "The server was overwhelmed by the massive demand. The only thing to do is wait."
At the same time, a German newspaper said one of its reporters had spoken to the reclusive owner of the collection, who had not been seen since the existence of the art works was revealed last week.
A statement from the national and Bavarian regional governments said 25 of the works would be displayed initially on the "Lost Art" site, which helps to establish the provenance of works seized by Germany's Nazi regime, mostly from Jews persecuted during the Holocaust.
The government has been heavily criticised - notably by families whose relatives were robbed by the Nazis - for keeping silent for almost two years about the trove of 1,406 European art works until a German magazine broke the story.
"It's too little, too late but at least it's a step in the right direction now," said Claudia von Selle, an attorney in Berlin specialising in art.
Defending their policy of silence, government officials said they were worried about the security of the art works and the related insurance, and that authorities were also conducting a confidential tax fraud investigation into Cornelius Gurlitt, in whose Munich apartment the art was found.
Works by Picasso, Chagall and Otto Dix were among those on the government's website, according to German media.
'I WANT MY PAINTING BACK'
In the United States, a retired lawyer who has a claim on one of the paintings, "Two Riders on the Beach" by Max Liebermann, told Reuters that he hoped to be able to get back the work, which belonged to his great uncle.
"I want my painting back, and soon," David Toren, 88, one of the two heirs of David Friedmann, said in a telephone interview on Tuesday. Friedmann was an industrialist from Breslau who owned the painting from at least 1905 to 1939.
"We have been looking for that picture for years."
Toren, who lives in New York, said he can still picture the painting that hung on the wall of his great uncle's villa before the war. Toren used to watch his father play skat, a German card game, in the next room.
Friedmann died in 1942. Toren escaped from Germany and spent the war years in Sweden. His older brother reached the Netherlands and now lives in London. Their parents perished at Auschwitz.
The Liebermann painting was among the first art works posted online from the Gurlitt stash.
Berlin lawyer Lothar Fremy said he had been searching for the work for about five years on behalf of Friedmann's two surviving relatives. Fremy said he filed a claim with German authorities last week after the work was featured at the press conference held about the cache.
"Legally it's very complicated," he said. But he urged the authorities to work quickly, given that his clients, Toren and his brother, are aged 88 and 92.
Markus Stoetzel, a lawyer representing the heirs of Alfred Flechtheim, a Jewish art patron and collector who lost everything to the Nazis, also welcomed the German move.
"Now more than ever it's time for Germany to do what it can to give justice to families of the Jewish victims whose art works were stolen by the Nazis from 1933 to 1945," he said.
The hoard is estimated to be worth up to 1 billion euros ($1.3 billion) and its legal status is likely to be contested. Customs officials stumbled on it during a routine investigation in Munich's smart Schwabing district in February 2012.
"The origins of the so-called 'Schwabing art trove' will be traced as quickly and transparently as possible," the federal and state governments said on Monday - over a week after news of the find was reported by the Munich magazine Focus.
"To establish transparency and to further expedite research into provenance, the first 25 works that are suspected to have been taken under Nazi persecution will be displayed on the www.lostart.de platform and that will be continuously updated."
The paintings, sketches and sculptures hoarded by the war-era art dealer Hildebrand Gurlitt, put in charge of selling confiscated "degenerate" art by Hitler, were found in the apartment of his 79-year-old son, Cornelius.
He told Germany's Sueddeutsche newspaper he had given documents relating to the art collection to the authorities.
"I have handed everything over to the public prosecution service," the newspaper quoted him as saying.
It said one of its journalists had met Gurlitt, who seemed to have vanished after the case became public, outside his flat in Munich, where he told her: "I am on the way to Wuerzburg to go to the doctor's. But don't worry, I'll come back soon."
The government's coordination centre for lost art said on the website that around 970 of the works were believed to have been confiscated, stolen or looted by the Nazis.
Some legal experts say Gurlitt may get to keep the art, but others say Germany could nullify his ownership. The governments said they had set up a team of six experts to examine the provenance of the works.
The federal government, which ordinarily leaves such cases to regional justice officials, stepped up its involvement after the United States asked it to publish a list of the art works. (Additional reporting by Michelle Martin; Editing by Mark Heinrich and Giles Elgood)