OTTAWA, March 22 (Reuters) - Canada's banking regulator is limiting the number of highly leveraged loans in the banks' residential mortgage portfolios, which have ballooned alongside rising prices to make Canadian borrowers among the most highly indebted in the world, the Globe and Mail reported on Friday.

The Office of the Superintendent of Financial Institutions has told lenders they will have to limit loans to borrowers with mortgages greater than 4.5 times their annual income, the newspaper reported, citing two sources familiar with the matter.

(Reporting by Ismail Shakil in Ottawa, editing by David Ljunggren)