ALBANY — A Democratic congressman who represents New York City wrote a letter endorsing an illegal spring break trip to Cuba taken by a group of Upper West Side public high school students accompanied by their history teacher.

Three days before the start of the trip, Rep. Jerrold Nadler sent a letter to the Beacon School teacher, Nathan Turner, saying he was “pleased” to learn of the nine-day journey, which he described as a “unique opportunity for cultural exchange.”

The trip, which was chaperoned by Mr. Turner and organized by a left-wing community group in Manhattan, violated federal travel restrictions to Cuba prohibiting high school educational trips to the communist dictatorship. The teacher led the students to Havana despite being denied permission by the education department, which is investigating the trip.

Mr. Nadler is the second New York politician known to have supported the tour with a reference letter intended to be helpful in case the students and their teacher ran into problems inside the country.

Lieutenant Governor David Paterson, whose stepdaughter participated in the same school trip in 2005, gave his stamp of approval in a very similarly word letter.

Both politicians say they were unaware at the time of giving their endorsement that the trip violated the federal travel ban, and that they assumed it was properly licensed.

Written on official stationary, both letters are dated March 29 and said the students would discover what it means “to be a global citizen” by visiting the island.

A spokesman for Mr. Nadler said via e-mail that the congressman “wrote a generic support letter to the teacher himself, at his request, as we would have for any in-district teacher requesting a supportive letter for a bona fide educational endeavor. The teacher represented to our staff that the trip was school-sponsored, as it apparently had been past years, and properly licensed.”

Mr. Nadler’s letter was released by the congressman’s office yesterday.

Mr. Turner has not been taken out of the classroom at Beacon School, as school investigators look into the circumstances behind the trip and whether his actions merit sanction. School officials say Mr. Turner was denied permission to take the students to Havana, and they are trying to determine how the teacher was able to travel anyway.

The teacher has chaperoned students to the island for the past several years, each time apparently without education department or federal approval. The federal government, which tightened its travel ban to the island in 2004, does not allow students at high school level or below to visit the island, even if the tour is supposed to be educational. Those who violate the ban can face fines of up to $65,000.

The trip, which took place between April 1 and April 10, was organized by the Interreligious Foundation for Community Organization/Pastors for Peace, located on West 145th Street. The group’s Web site says the Bush administration “does not want you to know the truth about the Cuban people.”

The site says the Cuban people are “a healthy people, with free health care, who live on average to age 77 — the same as the same as those in the U.S. — yet some die prematurely and many others suffer unnecessary pain because the blockade denies them access to many of the world’s medicines.”

At a press conference yesterday, Governor Spitzer said Mr. Paterson’s letter to the teacher was not inappropriate because Mr. Paterson was not aware that trip was not authorized. “I am persuaded that whatever David did was appropriate based on his understanding of where things were,” he said.

Asked whether the trip would have been worthwhile were it legal, a spokeswoman for the governor, Christine Anderson, said Mr. Spitzer, who has three daughters, would not want to “weigh in” because it was a trip “that his children didn’t take.”

Mr. Paterson said yesterday he would not have signed off on the trip had he known about the travel ban. “Under the law, it certainly seems inappropriate that they would have gone without a license to travel,” he said.

He said, however, that he is skeptical about the wisdom of the travel prohibition, saying his stepdaughter’s experience provided her with a sophisticated first-hand understanding of the communist nation.

“If the federal government is doing it because they don’t think being educated about communist dictatorships is important, perhaps what prevents communist dictatorships from spreading is that people learn what they are actually like,” Mr. Paterson said. “An educational trip I would see as a good thing.”

Assuming the federal government had authorized the teacher to take the students to Havana, Mr. Paterson contacted the education department urging school officials to give their permission. He said he was “disturbed” to learn that the department had not sanctioned any of the previous trips.

The trip reportedly included interviews with a 15-year-old prostitute and a homeless man, and a trip to a jazz club. Mr. Paterson and Mr. Nadler said in their letters that students would expand their knowledge of the country by visiting “museums, schools, and community groups.”