Newly disclosed letters written by the father of Anne Frank illuminate his desperate attempts to get the family out of the Nazi-occupied Netherlands.

The YIVO Institute for Jewish Research, a New York-based institution that focuses on the history and culture of Eastern European Jews, said yesterday that it had discovered the file among 100,000 Holocaust-related documents about a year and a half ago.

“We have come across the file which belonged to Otto Frank, documenting his efforts to immigrate his family and get them out of Holland,” said Cathy Callegari, a spokeswoman for YIVO, which is to release the letters on Feb. 14. Time magazine first reported on the letters yesterday on its Web site.

Ms. Callegari called the Otto Frank file “very rich, compelling and revealing, and we felt it had enormous historical content. It had never before been revealed or known.”

She said the institute waited to announce its discovery because of the need to explore copyright issues and the complex process of documenting the papers.

“We were given that file along with 100,000 other documents related to the Holocaust,” she said. “When you find a personal piece of correspondence, you can’t just release it because there are copyright laws.”

“When our team of lawyers recently rendered their decision, we hired Holocaust experts to study the files, to help people understand what the political climates were in the U.S. and Europe, and their policies regarding immigration,” she added.

The letters were initially held by the Hebrew Immigrant Aid Society in New York, which began transferring its archives to YIVO in 1974.

Ms. Callegari said the society’s archives consisted of documents from various agencies, and therefore the true origin of the Otto Frank letters may never be known. She said a volunteer archivist at YIVO had discovered the letters.

The disclosure came as a surprise to Bernd Elias, Anne Frank’s cousin and the president of the Anne Frank Foundation in Basel, Switzerland. The organization, established by Otto Frank, holds the rights to Anne Frank’s writings, according to its Web site.

Mr. Elias said he had asked about the letters but never got a direct answer about their nature. He said YIVO had never asked the foundation about rights to the letters.

“Of course I’m interested in them,” he said. “We would love to have them in our archive. I mean, we are the heirs of Otto Frank.”

Ms. Callegari said the documents included letters that Otto Frank had written to relatives, friends and officials between April 30 and Dec. 11, 1941, when Germany declared war on the United States.

The Frank family’s hiding place, a secret annex in an Amsterdam canal-side warehouse, has been turned into a museum. Patricia Bosboom, a spokeswoman for the museum, Anne Frank House, said the letters fit the general picture of what was known about Otto Frank’s efforts to get the family out of Europe.

The letters document how he tried to arrange for his family — his wife, Edith; his daughters, Margot and Anne, and his mother-in-law, Rosa Hollander — to go to the United States or Cuba.

He failed, and 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.

She died of typhus at age 15 at Bergen-Belsen, Germany, in 1945. Her father survived, returned to the Netherlands to collect her notes and published them in the Netherlands in 1947. “The Diary of Anne Frank” has sold an estimated 75 million copies.

Copyright 2007 The New York Times Company