Iranian physicist M. Hadi Hadizadeh was looking forward to returning to his alma mater, Ohio University, as a visiting professor.
He was a specialist in scanners for medical research and airline luggage screening, and a leading advocate of democracy in his country. He was once freed from an Iranian prison through the appeals of several Nobel laureates.
But a seemingly routine request for a US visa launched him on a 17-month nightmare, he contends, because of three words: "Iranian nuclear physicist."
"They thought I was either a double agent, or it wouldn't be safe for the security of the United States that an Iranian nuclear physicist would come here and do research," he said.
Hadizadeh was blocked by stringent visa requirements enacted after the terrorist attacks of Sept. 11, 2001, to bar scientific visitors who might hand over strategic knowledge and technologies to US enemies.
But the rules have become so broad that thousands of foreign students and scholars have been denied or delayed visas even though they have no connections to sensitive technologies.
The foundation of the new procedures is a government technology watch list that identifies scientific fields with potential military importance. Anyone studying those areas can be screened for months before being allowed to enter the United States, even if they have previously studied or worked in the country for years.
The list naturally includes research areas with clear military significance, such as biological weapons, navigation, and laser technology. But it also sweeps up whole fields of science that have both peaceful and military uses.
It now includes all of microbiology, much of chemistry and physics, even areas such as urban planning, landscape architecture, housing, and civil engineering.
"It seems to be an issue out of control," said Bruce Alberts, director of the National Academy of Sciences, considered the nation's preeminent scientific society. "It's a wonderful way of helping our enemies by insulting our friends."
The government concedes the rules have inconvenienced visa applicants. But State Department spokesman Stuart Patt said, "We have to put national security interests first."
The need for restrictive visa precautions is made evident, said advocates of immigration reform, by the fact that several of the Sept. 11 hijackers entered the United States on student visas.
"We need to be vigilant about who we are letting in here and what sort of information they are picking up," said Ira Mehlman, spokesman for the Federation for American Immigration Reform, which seeks to restrict immigration for economic and security reasons.