BANGOR, Maine — A third man who worked at a Calais hardware store has admitted to illegally selling guns to a Canadian man.

Leo Blais, 65, of Calais pleaded guilty Tuesday in U.S. District Court to conspiracy to provide guns to a person who is not a resident of Maine.

Charges against Blais and at least four others were the result of a joint operation of agents from the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives and the Royal Canadian Mounted Police. It was designed to curtail the flow of guns into Canada from Maine.

Blais admitted Tuesday to selling 20 guns between March and December 2006, either directly or through another person, to a Canadian while he worked at Johnson’s True Value Hardware in Calais.

So far, five men have pleaded guilty to charges as a result of the investigation. Assistant U.S. Attorney Joel Casey, who most often handles drug cases filed in federal court in Bangor, declined Wednesday to say whether more people could be charged in the gun smuggling scheme or if it was connected to drug trafficking.

Bruce Thibeault, 34, of Calais was sentenced to a year and a day in federal prison and ordered to pay a $2,000 fine after he pleaded guilty to a similar charge. Kurt Carter, 42, of Alexander was sentenced to 2½ years in prison after pleading guilty to a similar charge. Both men worked at the hardware store during the same time period that Blais did. They were sentenced in December.

The investigation that led to Johnson’s True Value Hardware apparently began in June 2006, when the owner of a Machias gun shop canceled the sale of eight 9 mm pistols to Lawrence Sears, 63, of Perry. The Machias store owner, according to court documents, alerted the ATF that he suspected the man was buying guns for another individual.

In an interview with investigators, Sears admitted that he had tried to buy guns in Machias for Andrew Porter, 34, of St. Stephen, New Brunswick. He also said that he bought guns in June 2006 for Porter in Brewer.

Sears was sentenced in August to 18 months in federal prison after pleading guilty to making false statements on an application to buy guns. Porter was sentenced in September to 2½ years in prison after pleading guilty to buying and possessing guns illegally.

Blais, like the others who worked at the hardware store, faces up to five years in prison and a fine of up to $250,000. In his plea agreement with prosecutors, Blais agreed to waive his right to appeal his sentence to the 1st U.S. Circuit Court of Appeals in Boston if his sentence does not exceed 12 months.

A sentencing date has not been set.

Blais remains free on personal recognizance bail.