(Adds details on oil and potash price estimates, further forecasts)
Feb 29 (Reuters) - The resource-rich Canadian province of Saskatchewan said on Monday that its projected budget deficit would be larger than previously estimated, boosted by a drop in oil prices that trimmed government revenues.
The province's 2015/16 shortfall, its first in two decades, will reach about C$427 million ($315.8 million), up sharply from C$262.2 million forecast in November. The fiscal year runs from April through March.
Canada's biggest wheat-growing province expects to return to a surplus by 2017/18, after running a smaller deficit next year, Finance Minister Kevin Doherty said in a statement.
Until this year, the province remained in the black even as most others ran deficits when their economies slowed. Premier Brad Wall's right-leaning Saskatchewan Party government faces an election in April.
Revenue from non-renewable resources -- which include production of oil and the crop fertilizer potash -- looks to fall C$617 million this year, according to the government.
The province will aim to maintain overall spending increases at 2.3 percent annually, Doherty said.
Saskatchewan expects to spend about C$14.3 billion for the year ending March 31, and collect roughly C$13.9 billion in revenue, a drop of C$158.4 million from the previous estimate.
The government estimates the price of West Texas Intermediate oil to average $44.78 per barrel in 2015/16, down from the $49.50 assumption it made in November, and the budgeted $57.15 per barrel.
The province sees potash prices averaging $267 per tonne in 2015/16, down from the $282 per tonne it forecast in November.
Saskatchewan's public debt is forecast to rise to C$13.5 billion by March 31 from C$11.7 billion a year earlier.
Its operational debt, which excludes debt held by government-owned corporations, health authorities and school divisions, is expected to move up to C$4.1 billion from C$3.8 billion. ($1 = 1.3523 Canadian dollars) (Reporting by Rod Nickel in Winnipeg, Manitoba; Editing by Chris Reese and Alan Crosby)