More overseas students are studying graduate physics in the United States than Americans, it has been revealed.
The news has prompted moves to impose quotas on applicants from abroad and to offer financial stipends to attract nationals.
Critics complain that US taxpayers are subsidising foreign scholars they believe will go back to their native countries with skills they can use to compete with the US. Universities, however, argue that it is easier to find overseas physics students than Americans, who are hesitant to make the commitment of time and financial resources needed to receive a doctorate in the sciences.
"US physics departments have had difficulty attracting US students to their programmes lately," said Patrick Mulvey, chief researcher for the American Institute of Physics.
"There's a big time investment. To come out and not necessarily earn the dollars doctors and lawyers earn - that makes it a hard sell."
Mr Mulvey traces the decline to the early 1990s when, because of the recession, academic and industrial posts for physicists dried up.
"It takes a while for that sting to go away," he said. Even now, "hordes of academic positions haven't opened up. There isn't a clamouring for physics professors where, on the other hand, students coming over from abroad aren't necessarily dissuaded by that job market phenomenon."
The number of US citizens enrolling as first-year graduate physics students last year fell to 1,500, the lowest level since the statistics started to be kept in 1965 and down from a 3,000 high.
Meanwhile, the number of foreign students has risen to more than 1,500, up from about 700 during the same period.
Part of the increase is attributed to the 1980 decision by China to allow its nationals to study in the US. They now make up 20 per cent of international students in US physics programmes.
Pennsylvania State University, where at least one physics professor has hired a tutor to help his students with English, is offering a cash bonus to attract Americans to its physics programme.
The University of Tennessee has taken the opposite approach, setting quotas to limit foreign enrolment. Under the controversial policy, overseas students can represent no more than 20 per cent of the students in any graduate programme.
But even at Tennessee, the quota has had to be waived for physics, where more than 40 per cent of the enrolment is foreign. Other universities are believed to have unacknowledged quotas.
But international physicists are probably more of an asset than a liability, Mr Mulvey said.
"People say 'we've educated them and they take their education and compete with us'." But he added: "While they're here, these people contribute to the US research effort at what would be considered a fairly low cost. And for the ones who stay in this country, they're obviously very bright individuals who can contribute."