With an overhaul of South Portland High School scheduled to begin in April, officials are seeking design changes because of higher-than-expected construction bids.

Harriman Associates, the project’s architect, has been told to find ways this weekend to pare it down by $4 million. That’s the difference between the lowest bid and the amount of money the city has to spend.

Voters in 2010 approved borrowing $41.5 million, of which $39.3 million was expected to be spent on construction, said Superintendent Suzanne Godin. Bids from four contractors, unsealed Thursday, ranged from $43.2 million to $46.7 million.

Godin said the lead architect, Daniel Cecil, is working to determine why there are discrepancies between the original estimate and the lowest bid, made by PC Construction, a Vermont-based company with Portland offices.

Cecil couldn’t be reached for comment Friday.

Ralph Baxter, chairman of the building committee that’s overseeing the project, said fluctuations in prices for gas and asphalt make estimating the cost of construction difficult.

“It’s a little higher than we thought it might be, but it’s not unexpected or uncommon,” he said of the lowest bid.

The building committee plans to meet Monday to consider changes to the design. The South Portland Board of Education is scheduled to vote Wednesday on whether to begin negotiations with PC Construction.

Baxter said he expects the building committee to meet twice in early March to settle on a final contract. The contract will then need approval from the school board and the City Council, which Godin hopes will happen by March 19 “to stay on the project time line.”

Construction is scheduled to be completed by December 2014, said Godin.

The design, as approved by voters, would expand the floor area to more than 300,000 square feet — about 100,000 square feet more than the school has now. Renovations include tearing down an annex built in 1962, building a larger library and rebuilding the cafeteria.

The total cost of the project, including design and other fees, is estimated at $47.3 million. Money from a facilities reserve account and surplus funds in the school department’s budget, as well as energy performance credits, covered $5.8 million that’s not included in the bond. South Portland is getting no state money for the project.

Voters in 2007 rejected borrowing $56 million for a more extensive overhaul that included a second gym, an artificial turf field and more classroom space.

Even the scaled-down design is far too big, said Albert DiMillo, the leading opponent of the bond approved in 2010. Shaving off $4 million shouldn’t be a problem, he said.

“You could take $20 million out of that project easy,” said DiMillo.

Still, he said, he wouldn’t be surprised if the school department tried to dip into its budget surplus to meet PC Construction’s bid, though he believes it would be illegal to do so without residents’ approval.

Godin said she doesn’t know yet whether the school department has options other than adjusting the design.