Anne Frank's father sent desperate letters to friends and family in the United States pleading for financial assistance to help the family escape from the Nazi-occupied Netherlands, according to papers released Wednesday.

"I would not ask if conditions here would not force me to do all I can in time to be able to avoid worse," Otto Frank wrote to his college friend Nathan Straus in April 1941. "It is for the sake of the children mainly that we have to care for. Our own fate is of less importance."

The letters, along with documents and records from various agencies that helped people immigrate from Europe, were released by the YIVO Institute for Jewish Research.

The information documents how Frank tried to arrange for his family — wife, Edith; daughters Margo and Anne; and mother-in-law, Rosa Hollander — to go to the United States or Cuba.

Frank wrote to relatives, friends and officials between April 30, 1941, and Dec. 11, 1941, when Germany declared war on the United States. He tried to arrange U.S. visas for his family before they went into hiding, but his efforts were hampered by restrictive immigration policies designed to protect national security, Holocaust experts said.

He referred to those problems in his letters.

"I know that it will be impossible for us all to leave even if most of the money is refundable, but Edith urges me to leave alone or with the children," he said in another letter to Straus.

Frank first applied for immigration visas to the United States for himself and his family in 1938, reviving his efforts in 1941 — a move that may seem lax with what is now known about the Holocaust but was logical to Frank at the time.

"He preferred what seemed to him like the nuisances that encumbered an otherwise comfortable life under Nazi occupation in the Netherlands to the insecurity of a life as a double refugee in a new country, even if a new country could have been found," said David Engel, a professor of Holocaust studies at New York University.

Frank was unable to secure passage to the United States. There were nearly 300,000 names on a waiting list for an immigration visa. Also, since Frank had living relatives in Germany, he would have been unable to emigrate under strict immigration policies.

Frank's attempt to move his family mirrors the efforts of thousands of German Jews, said Richard Breitman, an American University professor who focuses on German and American intelligence history.

"Frank's case was unusual only in that he tried hard very late — and enjoyed particularly good or fortunate American connections. Still, he failed," Breitman said.

YIVO, a New York-based institution that focuses on the history and culture of Eastern European Jews, discovered the file among 100,000 other Holocaust-related documents about a year and a half ago. The institute did not immediately disclose the find because it had to explore copyright and other legal issues, said Cathy Callegari, a spokeswoman for YIVO.

Frank's attempts to arrange a route out of the Netherlands were unsuccessful. The family took refuge in July 1942, hiding for more than two years before being arrested. Anne Frank described the family's life in hiding in a diary that has sold an estimated 75 million copies. The Frank family's hiding place in a secret annex in an Amsterdam canal-side warehouse has been turned into a museum.

The letters were initially held by the New York City-based Hebrew Immigrant Aid Society, which gradually transferred its archives to the YIVO Institute in 1974. Callegari said that the HIAS archives consisted of documents from various agencies so that the true origin of the Otto Frank letters may never be known. She said a volunteer archivist at the YIVO Institute discovered Otto Frank's letters about a year and a half ago.

Anne Frank died of typhus at age 15 in a concentration camp at Bergen-Belsen, Germany, in 1945. Her father returned to the Netherlands to collect his daughter's notes and published them in the Netherlands in 1947.

Time magazine first reported on the newly discovered documents on its Web site last week.