Despite recent tensions over Iran's nuclear program, the United States and Iran quietly initiated a high-level cultural exchange this week with a visit to Tehran by the librarian of Congress, James H. Billington.

Billington said Thursday in an interview that talks between the long-standing foes were still at a "very preliminary stage about developing broad-ranging discussions." But he described his six-day tour of Tehran, the capital, and Isfahan, the country's second-largest city, as one of the most rewarding of his many trips abroad during 17 years at the Library of Congress.

"It's been a very interesting time and a fascinating trip," Billington said. "I've been treated extremely well."

Billington said he expected the chief of the Iranian National Library, Mohammad Bojnourdi, to visit Washington "as part of a normal exchange." A date for that trip has not been set.

Billington, a presidential appointee confirmed by the Senate, is the highest-level U.S. official to visit Iran and meet openly with Iranian officials since relations between the two countries were severed in 1980 after militant students took over the U.S. Embassy in the wake of the Islamic revolution. The visit was approved by the White House, and Billington was briefed by the State Department before he left, U.S. officials said.

Billington said the goal of his trip was to discuss acquiring Iranian publications.

"We have a large collection on the Middle East and Islamic world, and we want to expand our collection," he said. "We're a world library, but our collection is not what it should be. The trip seemed important given our collection deficit and because the amount of material Iran has published" since relations were severed.

Billington said he also met with top officials at Tehran's parliamentary library, toured the national archives and had talks with experts on topics including Iranian films, Sanskrit and Russian architectural influences in Iran. He discussed sonnets with Simin Behbahani, one of Iran's most famous female poets. And he consulted with architects about a new facility to house Iran's national library and archives, similar to talks in other foreign capitals. He also spent two days touring Isfahan, about 200 miles south of Tehran.

Since the revolution, the only higher-level visit to Iran took place during the Reagan administration, with the controversial secret arms-for-hostages diplomacy conducted by national security adviser Robert C. McFarlane and Marine Lt. Col. Oliver L. North.

Shortly after taking office in 1997, President Mohammad Khatami, a former head of Iran's national library, called for bringing down the "wall of mistrust" with the United States through cultural exchanges. But previous efforts, including reciprocal visits by wrestlers and filmmakers, had limited impact. And U.S. overtures have often been turned down by the Iranian government, notably an offer last Christmas by President Bush to send a high-level humanitarian delegation that included a member of his family.