As the political battle over same-sex marriage plays out in state capitals across the country, several California companies have emerged as the go-to players for opponents of the marriages. One of the companies, Mar/Com Services Inc., lists its business address here in San Francisco, a city well known for its large and politically active gay population.

When Maine residents opposed to a new law permitting same-sex marriage decided earlier this year to challenge it, they hired Mar/Com to do the production work for the television and radio advertisements.

Central to this cottage industry is Schubert Flint Public Affairs, a company based in Sacramento that headed the winning campaign for Proposition 8, a 2008 California ballot measure that outlawed same-sex marriage.

Frank Schubert, the company’s president, said it was “not like we took the California campaign and photocopied it and took it to Maine, but we took some of the things we learned.” He said same-sex marriage is not “what our firm is devoted to,” but rather “is one area that has been very active in the last couple of years.”

Maggie Gallagher, the president of the National Organization for Marriage, a group opposed to same-sex marriage, hired Schubert Flint to develop radio advertisements in New Jersey and New York and put together an advertisement featuring Carrie Prejean, the former Miss California USA, who has voiced her opposition to same-sex marriage.

The National Organization for Marriage has fought against same-sex marriage efforts in Maine and New York — where a bill to legalize the unions was defeated this month — as well as in New Hampshire, New Jersey and Washington, D.C.

“Other political consultants have also had success on this issue,” Ms. Gallagher said in an e-mail message. “But Schubert Flint Public Affairs is a highly regarded firm with a winning track record.”

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