As the war in Iraq steams ahead, many foreign students studying at American universities remain stranded in their home countries without visas. Unable to attend to their research projects, the students’ absences have, in some cases, delayed or derailed scientific efforts to combat chemical and biological terrorism, a study found this week.

Stuck in a “visa jam,” hundreds of student scientists — including some at Yale — have been unable to enter America, bringing their research on diseases such as AIDS and leukemia to a halt, according to a study by the Hartford Courant. The jam is the result of heightened security procedures for screening foreign visas, which the U.S. Department of State enacted in response to the Sept. 11, 2001, terrorist attacks.

The Courant found that over two dozen students and scientists at 20 American research universities have been significantly disrupted by the visa delays. It reported that most of the stranded researchers were already working in the United States and left the country for brief trips, but have not been able to return.

Heng Zhu, a postdoctoral fellow in Yale’s Molecular, Cellular and Developmental Biology Department, left for Beijing last April, expecting to resume his research upon his return to the United States. But after almost a year, Zhu still remains in Beijing without a visa.

“I am still waiting!” Zhu wrote in an e-mail from Beijing to the Courant.

Working on a $1.5 million National Institutes of Health study to isolate proteins in genes, Zhu was near completion on research that could potentially help fight diseases.

Neither Zhu nor Yale officials were available for comment Monday night.

State Department spokesman Stuart Patt said while he could not comment on Zhu’s situation specifically, many foreign students have been experiencing significant delays in obtaining visas.

“We are trying to find ways to shorten some of these delays,” Patt said. “Some of those who are subject to security reviews will find that it takes a little longer now than it used to. A great deal more effort has been put into the visa issuance process.”

Sen. Joseph Lieberman — the ranking member of the Senate Governmental Affairs Committee, which has jurisdiction over the Department of Homeland Security — has worked extensively on issues of homeland security but believes there is still much work to be done.

“[Lieberman] is keenly aware of the needs to balance legitimate security concerns against the advantages to academia and the economy,” Lieberman spokeswoman Leslie Phillips said. “All of his work on homeland security demonstrates what’s going on in American universities.”

After the 19 hijackers from the Sept. 11 terrorist attacks entered the United States on valid travel, business and student visas, the State Department stepped up its security and intensified its visa issuance policy.

But according to the Courant, many scientists and educators complain the State Department is using vague, arbitrary standards in issuing visas, trapping legitimate foreign researchers in a “frustrating backlog.”

While the number of visas processed at the State Department has dropped to 7.9 million from 10 million last year, the rate of denials has risen from 25 percent to 28 percent, the Courant reported.

Assistant Secretary of State for Consular Affairs Maura Harty said in a press statement that the department has unveiled a new effort to better communicate changes to U.S. visa procedures, an initiative entitled “Secure Borders, Open Doors.”

“We want to ensure that the visa application process is straightforward for people who want to come to the U.S. to study, visit and conduct business and that it prevents the entry of those who would do us harm,” Harty said.