Every head will have to do a masters in school management if the opposition Moderate party wins this year's general election.
Resources for training headteachers will be doubled to make this possible.
Currently a two-year waiting list has prevented half of heads from receiving the supposedly compulsory training.
Fredrik Reinfeldt, leader of Sweden's opposition Moderate party, and Sten Tolgfors, education spokesman, have condemned the the current system for not doing enough to prepare heads for the demands of their jobs.
Writing in the newspaper, Dagens Nyheter, they said: "School managers are central to the quality and development of a school. It is essential we put more resources into improving the training of headteachers, especially when one in two heads currently dooes not get a place on a training course."
The training of heads has come under scrutiny since Nordic neighbour Finland easily outperformed Sweden in last year's education ranking from the Organisation for Economic Cooperation and Development.
Jan Liljegren, who has been principal of TAby Enskilda gymnasium for two years, had to wait six months before joining the heads' training programme in May 2005. He said: "It's an excellent course. It takes up many of the important issues a school principal needs to be able to deal with."
The course takes 36 days over six terms. Each term, Mr Liljegren and his vice-principal Erik Drakenberg do an intensive week's training. During the year they also do assignments and reading tasks. "It's important that school principals have some kind of formal qualification for the job," said Mr Liljegren.
"After all, we're ultimately responsible for the quality of the education our students receive and the well-being of our staff, as well as the effective running of the school."
The Moderate party plans to double resources for the training programme and allocate a further 120 million kronor (pound;9m) to universities over the next three years to develop a masters in school management.
Hans Persson, chairman of the Swedish Head Teachers' Union, said his members had been calling for such changes for years. "The Moderate party has hit the nail on the head," he said.