The planned withdrawal of government support for the housing market may drive mortgage rates up, an expert said.

"Mortgage rates could rise 75 to 100 basis points" after the federal government pulls back its support this spring, Nicolas Retsinas, director of housing studies at Harvard University, said in an interview Tuesday.

About 90% of mortgages were guaranteed or securitized by government in the last quarter, he said.

The biggest threat could come to housing markets that are overbuilt, such as Las Vegas and south Florida, said Retsinas, a former head of the Federal Housing Administration and of the Office of Thrift Supervision.

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