By Jasmin Melvin

WASHINGTON (Reuters) - Political advertising contracts with broadcasters are moving from filing cabinets in television studio basements to the Internet for all to view.

The Federal Communications Commission adopted a rule on Friday that will force broadcasters to reveal online who is paying for campaign ads and just how much they are shelling out.

The data, to come initially from the four biggest TV broadcasters in the top 50 media markets, is expected to provide insight on campaign spending wars ahead of the November congressional and presidential elections.

"In this kind of day and age, this kind of transparency is a no-brainer and it's something that's needed," said Mary Boyle, spokeswoman for the Common Cause good-government group that supports the online disclosure effort.

The FCC agreed to the rule despite warnings from broadcasters who said the conversion will be costly and unfairly expose their advertising rates to rivals.

Republican Commissioner Robert McDowell dissented to portions of the order, sympathizing with the broadcasters' arguments.

TV stations have been making public records of campaign advertising buys and other community-related issues since 1938 as part of their public interest obligation.

These records include detailed information on who paid for political ads, key personnel of the groups buying ads, when political ads aired and rejections of requests to buy air time.

Obtaining these files is currently a time-consuming, labor-intensive task, requiring multiple trips to TV station studios and money to pay for photocopies of the documents.

Going forward, these documents must now be uploaded to a database hosted on the FCC's website, beginning 30 days after the rule receives approval from the Office of Management and Budget. The agency expects swift approval as the rule does not require new disclosures, just a new format.

The four biggest broadcasters are ABC, operated by Disney Co, CBS Corp, News Corp's Fox, and NBC, controlled by Comcast Corp.

Smaller operators and stations in smaller markets will have another two years to comply.

BURDEN VS TRANSPARENCY

Broadcasters unsuccessfully tried to get support on the currently 3-member FCC panel for a compromise proposal that would allow them to leave out specific ad rate data but disclose the aggregate amount of political spending by buyers.

"It makes no sense for us to be put at a competitive disadvantage when our competitors don't face those same sort of mandates," said Dennis Wharton, executive vice president of communications for the National Association of Broadcasters.

Republican Representative Lee Terry told reporters on Thursday that he did not think it was appropriate to put this added burden on broadcasters. He said he has some discomfort when a government agency gets involved in political subjects.

Public interest groups countered that access to the more detailed data was necessary to ensure broadcasters were following the letter of the law when it came to giving political candidates fair pricing and equal opportunities for air time.

"If you don't have access to this data in its granular form, there's no way to enforce it, there's no way to alert the FCC to a violation, and there's no way to tell if they are stacking the deck in the first place," said Free Press senior policy counsel Corie Wright.

The increased transparency comes as political spending has shot up in recent years, thanks to outside groups known as "Super PACs" that can raise and spend unlimited amounts to help politicians, as long as they do not coordinate with official campaigns.

These independent "super" political action committees have already spent nearly $104 million this campaign cycle compared with only $26.8 million spent in the same time period during the 2008 election.

The FCC said it would cost as little as $80 to $400 per station for broadcasters to begin uploading large paper files.

Democrat Anna Eshoo, who chairs the House Commerce subcommittee on communications and technology, has thrown her support behind the disclosure requirement and has blasted broadcasters' objections.

"The idea that broadcasters say this is going to cost money is laughable. Anyone here think that broadcasters are not going to do well in this political season with political advertising?" she said at a computer and technology industry forum on Thursday.

(Reporting By Jasmin Melvin; Additional reporting by Alina Selyukh; Editing by Tim Dobbyn)