Foreign students in the US could be barred from using some types of laboratory equipment or even setting foot in certain parts of research laboratories if two US government proposals aimed at tightening security are approved by spring 2006.

The proposals, put forward separately by the Commerce Department and the Department of Defense, would require universities to obtain special licences for foreign researchers working in some laboratories or on equipment that is subject to export restrictions, such as high-end oscilloscopes.

Universities and other institutions say that this would be all but impossible to implement. They argue that preventing security breaches should be part of the government visa process, not the job of higher education institutions.

"Security also requires that the US Government does not place well-intentioned but ill-conceived and unworkable restrictions" on university research, said Nils Hasselmo, president of the Association of American Universities, the organisation that represents leading US research universities.

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The association's concerns are supported by the Government's National Institutes of Health and National Science Foundation, the American Association for the Advancement of Science, the Association of American Medical Colleges, the Section of International Law of the American Bar Association and other groups that object to the proposals.

Placing more restrictions on foreign students - who already face long and costly delays and intensive scrutiny before being admitted to the US - "may seriously undermine the vitality of American research", Dr Hasselmo said.

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About one third of the 455,355 science and engineering graduate students in the US are non-Americans, of whom more than half are from Asia.

This means that the greatest number of foreign-born students in the most sensitive areas of study come from what the Government considers to be "countries of concern", including China, India, Israel, Pakistan and Russia.

But the universities say that students and scholars should be cleared during the visa process to conduct research in US laboratories using American equipment.

The Bar Association says there is no clear connection between the proposed licence requirement and improved national security, implying that it would probably be vulnerable to a legal challenge in the courts.

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In a statement, the AAAS said that the recommendations would "diminish our national security rather than increase it" by damaging the nation's economic competitiveness.