After two failed attempts to win a City Council seat, Dr. Jay Golub is changing his strategy in making his third run for public office.

In a move torn from Mayor Bloomberg’s playbook, Dr. Golub, a longtime Republican, is challenging Public Advocate Betsy Gotbaum – as a Democrat.

A dentist who lives in Gramercy, Dr. Golub, 36, has played a leading role in organizing Republican candidates. Six weeks ago, however, he switched parties and resigned from his posts as Republican district leader and vice president of New York County’s Republican Party.

Dr. Golub unabashedly admits that he switched his party affiliation to compete in next year’s election, saying the Democratic Party “is really the only place to play right now.” But he says he will never be a Republican again and insists that he will champion the issues he always has.

“I haven’t changed my issues, my issues are exactly the same,” he said yesterday during a phone interview. “The difference is, I’m running under a different banner.”

After several attempts at running uphill campaigns with what he said was a lack of help from the state party, he says he realized that many Democrats shared his penchant for conservative fiscal policy and more moderate social positions.

He has backed nonpartisan elections and says if he could run with a “blank” party affiliation he would. Without that option, he says this is the best fit. Next week he is holding his first fund-raiser to get his campaign going.

Dr. Golub has spent much time rallying Republican contenders for public office around the conservative “Urban Republican” platform of tax cuts, spending cuts, and phasing out rent control. In 2002, he helped launch an effort to help Republican candidates win seats in the city council.

At the time he was quoted in The New York Sun as saying: “We should be proud to be Republicans. It’s the issues where we disagree with Democrats that need to be the focus of our campaigns.”

Although it might be difficult for him to distance himself from past stances, he says that being pro-choice, in favor of restrictions on gun ownership, and for school-choice and voucher programs makes him an appealing choice for many voters in the middle.

“In the end I’m as much a Democrat as I am a Republican,” said Dr. Golub, who is backing President Bush in the presidential election. “I’ve been running as a Republican because I really believed that the fiscal side of my platform matched the Republican Party better…but I can’t even say that an issue that I firmly believe is Republican anymore.”

Not everyone buys the switch. A representative for Ms. Gotbaum, who will undoubtedly be the front-runner in the election, said it was a transparent attempt to fool voters.

Political consultant Hank Sheinkopf, who worked on the public advocate’s last campaign, said, “He cannot hide his Bush Republicanism under a voter-registration switch. Voters are much smarter than that. He’s switching his party affiliation simply to run for office. The guy has no core political beliefs.”

Dr. Golub’s campaign manager, Robert Hornak, a longtime political consultant, downplayed the change, saying centrists in New York have a difficult time fitting into party molds.

“A lot of people think that party loyalty should come first and I don’t agree with that,” Mr. Hornak said. “I have been a Republican my entire life and I think I’ve been extremely loyal to the party, but there is a greater cause. It doesn’t really matter whether it’s Republicans or Democrats or Independents carrying that message.”

Both Dr. Golub and Mr. Hornak said the state Republican Party has ignored candidates in the city.

A spokeswoman for the state GOP, Karin Kennett, yesterday called that characterization “perplexing,” saying the Party not only supports city candidates, but also just gave them center stage at the Republican National Convention.