Westbrook police on Saturday arrested a Windham man, who is registered sex offender, for allegedly supplying alcohol to a woman under the age of 21.

Police said they arrested Timothy W. Plummer, 48, after seeing him buy alcohol for 19-year-old Holly Pinkham of Windham at the Shaw’s supermarket in Westbrook.

Police stopped Pinkham’s car a short time after the purchase and arrested Plummer on a charge of furnishing alcohol to a person under age 21. Plummer is listed on Maine’s sex-offender registry as a sexual predator, police said.

Westbrook police summonsed Pinkham for illegal transportation of alcohol.

“That was definitely a good arrest for us,” said Westbrook Police Captain Tom Roth.

Plummer was released from Cumberland County Jail Sunday on $2,500 bail, jail officials said.

The arrests were part of a citywide underage-drinking enforcement effort in which four teams of two officers combed the city checking in on locations where minors have been consuming alcohol in the past, police said. The teams also monitored bars and stores that sell alcohol.

Police also visited the homes of juveniles who were on probation or had conditions of release. At one home police seized marijuana and drug paraphernalia from minors using the substance. One minor was also summonsed for possession of tobacco products.

“After looking at the Maine Youth Alcohol and Drug survey awhile back, we noticed Westbrook and other surrounding communities had high alcohol use among underage drinkers,” Roth said. “We have since noticed those numbers have dropped, which is a part of efforts such as this.”

The patrols were paid for through a grant from the Maine Office of Substance Abuse. Westbrook Police also have money from the Peoples Regional Opportunity Program of Portland and from Medical Care Development.

The enforcement details will continue periodically during the next two years.