PORTLAND — A longtime selectwoman’s apparent secret — that she can’t read or write — will become part of her defense and out in the open when fighting tax fraud and disability claims charges, her attorney said Thursday.

Carole Swan testified Wednesday during a suppression hearing in U.S. District Court in Bangor that she’s basically illiterate.

Swan’s inability to read much more than names and numbers will be a “fact of significance in her defense,” said Leonard Sharon, an attorney in Auburn.

Swan couldn’t have known if her and her husband’s tax returns understated their income because she didn’t have a full understanding of their taxes without being able to read, he said. Her inability to read also plays into whether she understood that certain work had to be reported when filing for federal worker’s compensation claims, he added.

“Her lack of reading ability affects her quantum of knowledge,” Sharon said.

Swan was indicted in early 2011 on federal charges for allegedly using her position as a Chelsea selectwoman to extort $20,000 from a local construction company. She’s also charged with tax fraud and making false statements to obtain worker’s compensation payments. Her husband, Marshall Swan, is facing tax fraud and other charges.

During Wednesday’s hearing, Swan made the unexpected statement that she couldn’t read or write for the most part.

That admission came as a surprise to former Selectwoman Sharon Morang, who said Swan never gave any indication that she couldn’t read or write in the three years they served together.

Selectpersons have to regularly read and sign the town’s bills before the town manager can pay them, Morang said, and she remembers Swan sending out campaign letters to voters over the years. When Swan was the council chairwoman, she had to prepare meeting agendas, she added.

Years ago, Swan worked for the U.S. Postal Service, Morang said, which would have required taking a civil service exam.

“She covered it well,” Morang said. “She made everybody think she was literate.”

Nobody answered the phone at Swan’s residence on Thursday.

Assistant U.S. Attorney Don Clark declined to comment on Swan’s testimony that she couldn’t read.

“If it’s an issue at trial, we’ll deal with it at trial,” he said.

About 7 percent of Mainers lack basic literacy skills, meaning they can’t read or write above the third-grade level, according to the National Center for Education Statistics.

Many people hide their lack of literacy skills from friends, employers, co-workers and even spouses and children, said Amy Schmitz, spokeswoman for ProLiteracy, a Syracuse, N.Y.-based nonprofit adult literacy organization.

“This is the kind of thing that feels to the individual like a stigma or something they should be ashamed of,” she said.

No trial date has been set for Swan. Sharon has filed motions seeking three separate trials on the different charges.