CAMBRIDGE, Mass. — When Alena Shkumatava opens the door to the “fish lab” at the Whitehead Institute of M.I.T., she encounters warm, aquarium-scented air and shelf after shelf of foot-long tanks, each containing one or more zebra fish. She studies the tiny fish in her quest to unravel one of the knottiest problems in biology: how the acting of genes is encouraged or inhibited in cells.

The work, focusing on genetic material called micro-RNAs, is ripe with promise. But Dr. Shkumatava, a postdoctoral researcher from Belarus, will not pursue it in the United States, she said, partly because of what happened last year, when she tried to renew her visa.

What should have been a short visit with her family in Belarus punctuated by a routine trip to an American consulate turned into a three-month nightmare of bureaucratic snafus, lost documents and frustrating encounters with embassy employees. “If you write an e-mail, there is no one replying to you,” she said. “Unfortunately, this is very common.”

Dr. Shkumatava, who ended up traveling to Moscow for a visa, is among the several hundred thousand students who need a visa to study in the United States. People at universities and scientific organizations who study the issue say they have heard increasing complaints of visa delays since last fall, particularly for students in science engineering and other technical fields.

A State Department official, who spoke on the condition of anonymity, said that delays of two or three months were common and attributed the problem to “an unfortunate staffing shortage.”

The issue matters because American universities rely on foreign students to fill slots in graduate and postdoctoral science and engineering programs. Foreign talent also fuels scientific and technical innovation in American labs. And the United States can no longer assume that this country is everyone’s first choice for undergraduate, graduate or postgraduate work.

Albert H. Teich, the director of science and policy programs at the American Association for the Advancement of Science, organized a meeting on the subject in January with representatives from the National Academy of Sciences and several dozen other scientific and academic organizations. Among other things, he said, the group will try to bring the issue to the attention of the new administration.

It would be hard to argue against security checks for foreigners coming to the United States to pursue high-level scientific or engineering work. And some experts argue that people from certain countries — China, India, Pakistan and Middle Eastern countries are most often mentioned — should be subject to additional scrutiny.