The Federal Communications Commission voted Wednesday to restart its review of restrictions on media ownership, two years after an earlier attempt to loosen the rules failed.

FCC Chairman Kevin Martin called the work a “vital process” concerning important issues. He promised the agency would approach the issue differently than it did last time, when a court blocked changes in the rules. He said the commission “should take into account the competitive realities of the media marketplace” while also striving to meet diversity goals.

Democratic commissioners Michael Copps and Jonathan Adelstein voted against parts of the FCC’s decision to re-examine the media ownership rules. They said that the FCC this time needs to weigh more carefully the impact of any changes on the number of different media voices available to local viewers and listeners. They said the agency should commit to giving the public a chance to comment again once a specific proposal is offered.

The FCC’s next rewrite of media ownership rules will determine how many media outlets a company can own in a single market. Media conglomerates such as Tribune have argued that ownership of multiple television stations, radio broadcasters, cable providers and newspapers in the same city helps them compete. Opponents say such concentration mutes diverse voices in the media.

Mr. Adelstein called the new examination of the rules “totally inadequate,” citing the FCC’s failure to commit to offering consumers a second chance to comment after the agency proposes new rules.

“We seem to be repeating past mistakes,” he said. “It’s like a blank check to giant media companies.”

Mr. Copps also voiced concerns. “If we make the wrong decision, our communities will suffer and our country will suffer,” Mr. Copps said. “On media consolidation, there are no red and blue states.”

Mr. Martin said the FCC research would examine how the public gets its news and information, competition across media platforms, marketplace changes since its last look, localism and potential impacts of changes on independent and family-friendly programming.

Mr. Martin indicated that the current FCC limit on newspaper-broadcast cross-ownership in a single market will be among the elements under scrutiny. The cross-ownership rule regulates companies’ ownership of newspapers and TV stations in the same market. (Some cross-ownership situations remain from a time before the rule was adopted.)

“I think the newspaper broadcast rule hasn’t had any changes since the 1970s, while a lot of the other rules have changed. I’ve been very public about thinking the commission needs to re-evaluate, but we are just beginning the process,” Mr. Martin said.

Consumer groups, which started out slow last time but eventually generated a record-breaking number of comments to the FCC, claim they will start out much stronger this time. They have launched both a lobbying effort aimed directly at Capitol Hill and a grass-roots effort aimed consumers.

One grass-roots effort from Consumers Union featuring a song and animation warning to “Resist the Tower! Fight Media Power!” was posted on hearusnow.org.