With contenders in national elections amassing support through social networking sites such as Facebook and MySpace, New York City candidates are increasingly turning to Internet hubs as an inexpensive way to reach voters.

Local candidates and political observers say a driving factor in this shift has been Senator Obama’s successful use of Web sites that allow users to become online “friends” with candidates.

“Clearly, what you’ve got is a revolution in political campaigning, both in terms of fund-raising and organization building, and the Obama campaign is the model for it,” a professor of public affairs at Baruch College, Douglas Muzzio, said. “In less than 10 years, it’s going to be de rigueur for any campaign.”

Mr. Muzzio said candidates for local offices, in some ways, have more incentive to use social networking sites than politicians running for national office.

“If someone is running for a local seat in Brooklyn, buying time on WABC is crazy, because you’re broadcasting into Long Island and New Jersey. You need to target people more directly,” he said. “The people who look at your Facebook page have connections to you and similar interests.”

Setting up a profile on Facebook or MySpace is also free.

“It’s a cheap way, you’ve got to admit, to reach out to people,” Council Member Tony Avella, who is running for mayor in 2009, said. “It helps independent candidates like myself.”

The Queens council member’s MySpace profile is simple: It contains a photo of him, a biography, his stance on various issues, a Web log with updates on his campaign, and his zodiac sign.

Other candidates’ pages are more complex. Paul Newell, who is running for state Assembly against Speaker Sheldon Silver, lists his favorite musicians and movies on his Facebook profile. Council Member David Yassky, who is running for state comptroller, has a section on his MySpace profile that allows users to make donations.

But visitors should beware: Candidate profiles might be frauds.

An elaborate Facebook profile for Council Member John Liu, a likely candidate for higher office in 2009, was not created or condoned by his staff, he said. Mr. Liu blamed its existence on how “spontaneous and uncontrollable” the Internet is.

Mr. Avella hired a consultant to create and maintain his MySpace profile. Such distance between a candidate and his or her online persona is common among local candidates: Some are barely aware of how their profiles work but still see them as necessary.

A candidate for public advocate, Norman Siegel, said he was unaware of a Facebook page that allows users to register themselves as supporters of his campaign. He said he later discovered that a volunteer for his campaign had set it up.

“It’s not my world, but I’m trying to understand it because, for a lot of younger people, it’s their world,” Mr. Siegel said.

The president of Brooklyn, Marty Markowitz, who is a possible candidate for mayor in 2009, called himself a “reluctant participant” in his own profile on Facebook.

“My staff says it’s essential,” he said. “If it’s a way to communicate, then why not have it? Other than that, I haven’t got a clue.”