CAMBRIDGE, Mass. (AP) Former congressional candidate John O'Connor, an environmental advocate and real estate developer, died after suffering a heart attack while playing basketball at the Cambridge YMCA on Friday. He was 46.

O'Connor was chairman of Gravestar Inc., a development firm, and founded Greenworks, which served as an incubator for environmental start-up companies, offering venture capital, low rent and shared utility costs at an East Cambridge facility.

O'Connor, a Cambridge resident and Democrat, lost a 1998 congressional bid for the 8th District seat vacated by Joseph Kennedy. U.S. Rep. Michael Capuano won.

O'Connor was a basketball enthusiast and played at Clark University in Worcester. His interest in environmental issues was sparked in college. He learned that Raybestos, an asbestos manufacturer in his Connecticut hometown of Stratford, Conn., had built a baseball field atop its former dump.

O'Connor founded the National Toxics Campaign and lobbied Congress in the 1980s for passage of the Superfund law, which provides funds to clean contaminated sites.

''John O'Connor's entire life was spent focusing on the public good,'' Cambridge Mayor Anthony Galluccio said.

''John impacted hundreds and hundreds of people's lives locally and was active in virtually every local charity and cause that I can think of, especially those that involved children,'' Galluccio said.

O'Connor was married to Carolyn Mugar, heiress to the Star Market fortune.

He also founded the Irish Famine Memorial Committee, which raised funds to build on Cambridge Common in 1997 the first such memorial in the United States. Former Irish President Mary Robinson dedicated it.

O'Connor leaves his wife, a stepdaughter, Chloe; brothers James of Saugus and Jeff of San Diego; a sister, Emily of Washington D.C.; and his parents, Kay and George O'Connor of Stratford, Conn.