BANGOR, Maine — A Whitefield contractor testified Tuesday that he paid three kickbacks to Carole Swan when she was a Chelsea town selectwoman, and his construction company had a contract to plow and sand the town roads.

Frank Monroe took the stand shortly before noon Tuesday on the opening day of Swan’s trial in U.S. District Court on extortion charges. Swan has said she was running an independent sting operation to prove Monroe was bribing public officials.

Direct examination of the contractor is scheduled to resume Wednesday before a jury of seven men and seven women including alternates.

Monroe said that his firm had the plowing contract between 2006 and 2011. He said that typically his firm had to bid in even numbered years on two-year contracts.

Monroe testified that in 2008, he talked to Swan but no other selectmen about the possibility of extending the contract by negotiating it rather than by having to bid on it.

“Carole was the one that ran the show,” Monroe said in response to a question about why he dealt only with Swan. “She was the one that handled it all.”

Assistant U.S. Attorney Donald Clark, who is prosecuting the case, described Swan, 55, of Chelsea, as a “corrupt elected public official” in his opening statement Tuesday. He said that Monroe paid Swan two kickbacks in order to keep the contract but went to police when she told him to overbill the town for sand, then, pay her the $10,000 overpayment.

Clark also said that the other selectmen agreed in 2008 to extend Monroe’s plowing contract for one year. Swan switched the paperwork and surreptitiously had selectmen sign a two-year contract.

Defense attorney Leonard Sharon of Auburn did not make an opening statement. Sharon said he would speak to the jury after the state rests its case.

The attorney said late Tuesday after court adjourned for the day that Swan would testify in her own defense.

In his trial brief, filed Aug. 30, Sharon said that he would present evidence that Swan “was approached on numerous occasions by the contractor, Frank Monroe, asking her to secure favorable contracts and offering kickbacks.” The attorney also described his client as a woman who endured years of abuse at the hands of her husband, Marshall Swan.

“Based on this evidence, the defense will ask the jury to consider that the domestic abuse created in Carole a propensity to tell male authority figures what she believed they wanted to hear and to accept personal blame for events when being accused of wrongdoing, even when she was without fault,” Sharon wrote.

Through his attorney, Walter McKee of Augusta, Marshall Swan has denied the abuse allegations. He has not been charged with a domestic violence crime.

Swan was indicted in February 2012 on three counts of violating the Hobbs Act. It defines extortion as “the obtaining of property from another, with his consent, induced by wrongful use of actual or threatened force, violence, or fear, or under color of official right.”

Because Swan was a selectwoman when she allegedly received kickbacks from Monroe, she was charged under the “color of official right” section of the federal statute, according to court documents.

The prosecution will present evidence that Swan had the town overpay Monroe in exchange for a $3,000 kickback in January 2010 and $7,000 in December 2010, Clark said in his opening statement. In the third count, she allegedly asked Monroe in January 2011 to inflate his bill for road sand so she could get $10,000.

The trial is scheduled to end Tuesday, Sept. 17.

Earlier this year, U.S. District Court Judge John Woodcock severed Swan’s trial on the extortion charges from her trial on tax and workers’ compensation fraud charges. He also ordered the husband and wife be tried separately after the abuse allegations surfaced.

Marshall Swan is to be tried next month on tax fraud charges.

Carole Swan was found guilty by a federal jury in July on five counts of tax fraud from 2006 to 2010 and two counts of lying in 2008 and 2010 about her income and work history to receive workers’ compensation benefits.

The jury rejected Swan’s contention that she was justified in breaking the law because of alleged abuse at the hand of her estranged husband.

Swan was found not guilty on two of four counts of workers’ compensation fraud and not guilty of the illegal use of federal funds to pay for a culvert with Federal Emergency Management Agency money.

If Swan does not take the stand, the jury will not learn of her convictions, Woodcock ruled Monday. If she does take the stand, the prosecution may introduce those convictions to impeach her testimony.

If convicted of extortion, the most serious charge of which she has been accused, Carole Swan faces up to 20 years in federal prison. On the charges of which she has been convicted, Swan faces up to three years in prison for tax fraud and up to five years for workers’ compensation fraud.

In addition to prison time, she could be ordered to pay fines of up to $25,000 on each count and to repay workers’ compensation funds she illegally received.