HALIFAX - NDP Leader Jack Layton made a billion-dollar promise Monday to fix the health care system once and for all -- a vow quickly dismissed by the Conservatives as too costly.

Speaking at Dalhousie University's medical school, Layton said an NDP government would spend an average of $200 million a year to increase training spaces and help provinces expand their medical schools.

The aim, Layton said, would be to boost the number of new nurses and doctors by 50 per cent to address a shortage that has left five million Canadians without a family doctor.

"It's time to directly address this problem," Layton said.

"Fully phased in, our program will increase the number of doctors being trained by 1,200 a year."

Layton also promised additional money, later estimated by party officials at $125 million a year, to forgive student loans for graduates who agree to practice family medicine for at least 10 years.

That spending would only kick in after four years, when the new students start to graduate.

"We met with students last year, a great many of whom would have liked to have been family doctors, and (who) told me very simply that they had to go on and become specialists because by staying as family doctors, they would be unable to pay their student loans," Layton said.

In Ottawa, Prime Minister Stephen Harper called Layton's promise high-priced.

"NDP promises always sound good but the economy has to be able to afford them," Harper said.

"(With) the NDP, it's far from clear where they would get all this money to spend billions and billions of dollars at a time of economic uncertainty."

Layton accused Harper of breaking a promise in the last election campaign to make health care a top priority. He invoked the name of former NDP Leader Tommy Douglas, a pioneering former Saskatchewan premier hailed as the father of medicare, as he promised a federal NDP government would protect publicly funded care.

Layton also promised to work with the provinces to help foreign-trained doctors receive credentials in Canada.