VANCOUVER (Reuters) - Canada's provinces agreed in principle on Monday to support a compromise plan to expand the country's national pension plan that would see premiums raised moderately over time to provide greater payouts for Canadian pensioners.

The proposed changes, if formally approved by the provinces, would start in 2019 and be phased in over seven years, according to the plan signed by eight provincial finance ministers and federal Finance Minister Bill Morneau.

Reforming the Canada Pension Plan, or CPP, requires the support of the country's federal government plus seven of the 10 provinces, representing two-thirds of the Canadian population.

The refusal of the previous federal Conservative government to change the plan prompted Ontario's Liberal government to come up with its own plan to boost retirement security for residents in the absence of a national solution.

The proposed changes, revised from Ontario's proposal, will now be considered by the provinces and, if approved, could be formalized within weeks.

(Reporting by Julie Gordon; Editing by Leslie Adler and Peter Cooney)