Cambridge residents voting in Thursday’s primary will determine the next state representative from the 25th Middlesex District, the only Congressional district wholly contained within the Democratic stronghold of Cambridge. The winner among the three Democrats competing in the primary will run unopposed in the general election since there is no challenger from the Republican party.

Voters said they expect that Cambridge City Councillor Marjorie C. Decker will win the primary and with it the seat.

Local pundit Robert Winters went so far as to estimate her chances of winning the election at “101 percent.”

Decker’s opponents are Gayle E. Johnson, an active volunteer in Cambridge, and Lesley R. Phillips, the chair of the Ward 6 Democratic Committee in the city who holds a master’s degree from Harvard Divinity School.

The seat is currently held by Alice K. Wolf, who announced that she would not be running for reelection last March. Decker, who declared her intention to run hours afterwards, worked for Wolf as a legislative aide and later as her campaign manager. She has received public support from Wolf and many of her fellow city councillors in her congressional bid.

“She’s very passionate, she’s very smart, she’s got great progressive values, and I think she would do a great job in this seat,” Wolf said. “I hope she wins the race.”

Glenn S. Koocher ’71, a former member of the Cambridge School Committee, said that Decker has the most visibility among the three contenders.

“She’s well known, outspoken, and aggressive for making her feelings known. She has the advantage for being out there,” Koocher said.

Michael Kenney, a retired Boston Globe reporter and a resident of Cambridge, remembered that at the beginning of the Iraq War, Decker made a practice of reading the names of American soldiers killed in Iraq during City Council meetings.

“She would not only ask for a moment of silence, but for permission to read the names of the soldiers killed in action. She’s always been very strong on the veterans, always been very strong on the unions,” he said.

Her opponent Phillips serves on the board of Citizens for Participation in Political Action and is also a member of the city’s Gay, Lesbian, Bisexual, and Transgender Commission. She has campaigned on issues including single-payer health care, affordable housing, and environmental sustainability.

Kenney recognized Phillips as “certainly the serious challenger,” and noted that Johnson “has not made much of a presence.”

Phillips said, “I see myself as an independent voice to get some things done in the district and the Commonwealth. I’m not interested in my future positions.”

Johnson, who is blind, serves as the chair of the Cambridge Commission for Persons with Disabilities and volunteers for a crisis intervention hotline. She also works as a community organizer for the Massachusetts Alliance of African People and previously worked on Beacon Hill as an aide in the House and the Senate.

Decker and Johnson did not return requests for interviews.

—Staff writer Kerry M. Flynn can be reached at kflynn@college.harvard.edu.

—Staff writer Maya Jonas-Silver can be reached at mayajonas-silver@college.harvard.edu.