Politics Keeps Scholars Out of U.S., Critics Say

Withholding visas is said to endanger America's intellectual freedom

For nine months, Riyadh Lafta, an Iraqi professor of medicine, tried to get a visa to visit the University of Washington, where he had been invited to share his research on the unusually high rates of cancer among children in southern Iraq.

But by last March, with no visa forthcoming, the American institution came up with an alternative plan. Mr. Lafta would deliver his lecture at Simon Fraser University, in Vancouver, British Columbia, and it would be broadcast by video to a public