Douglas Weir, dean of the education faculty at Strathclyde University, revealed that despite three applications for every place at the Jordanhill campus this session, next year's ratio is likely to be two to one (800 candidates for just over 400 places). "That is worrying," Professor Weir said.
The problem will be exacerbated by "a badly skewed recruitment pattern" in which students wishing to teach history and biology are easily found, but computing, physics, geography, technology and - increasingly - music and art face mounting difficulties.
Professor Weir told secondary heads at their annual spring conference in Battleby: "We can oversupply you with teachers in subjects that are still popular, and we can undersupply you with teachers in subjects where recruitment has traditionally been difficult."
New Scottish Office regulations that require prospective secondary teachers to have graduated after studying their main subject for three years instead of two, while welcome, would cut down applications still further. Jordanhill's figures show a quarter of this year's secondary students would not have been eligible for entry.
"We have to start working very hard to make teaching attractive over the next few years," Professor Weir said, "and that means giving teachers time to think."
The key question for policy-makers was: "Do you want good teachers or do you want enough teachers?" The Scottish Higher Education Funding Council, which sets teacher intake figures on Scottish Office advice, moved last month to increase the number of entrants next session to 1,000 for the secondary postgraduate course. Intakes will have to remain at that level - 200 up on this year's figure - for at least the next 10 years.
Professor Weir said he was concerned that quality in teacher education was being compromised by underfunding, particularly as student placements added to costs.
He also said there were too many subjects requiring initial training, with continuing pressure for more.
Professor Weir suggested that 12 weeks on school placement out of the 36-week course would be sufficient instead of 18. Government policy should also emphasise education not training, leadership not management, improvements in pupil-teacher ratios and "qualitative as well as quantitative measurement".
He said: "If we educate teachers better, they are likely to have a more credible knowledge base. If teachers have a credible knowledge base, they can become more trustworthy to Government. If they see themselves as trusted, their self-esteem and morale will rise.
"We then have created a virtuous cycle in which the external and unpopular imposition of targets and indicators and competences and all the other signs of a nation which feels it has to control its teachers become unnecessary."