The survey, released Monday, said ABC, CBS and NBC used religion either to portray GOP candidates as zealots or to exaggerate the differences in their faith.
The Media Research Center's Culture and Media Institute examined network news reporting on Republican candidates and religion from Jan. 1-Oct. 31 and compared it to coverage of the Democratic presidential primary candidates during the same period in 2007.
The MRC -- a conservative watchdog organization based in Alexandria, Va. -- says on its Web site its mission is to educate the public and media on bias in the media.
"The discrepancy, in both the amount and tone of the coverage, is striking," the center said in a release. "Network reporters, so disinterested in the beliefs of [President] Obama and his rivals for the 2008 nomination, take every opportunity to inject religion into their coverage of the GOP field."
In the 2008 election, media reported on questions raised about whether Obama, a Christian, was Muslim, even on his being taken task to for attending church where a minister preached incendiary rhetoric.
The study found ABC, CBS and NBC mentioned GOP candidates' religion 143 times in the first 10 months of 2011, compared with mentions of Democratic candidates' faith 19 times during the same period of the 2008 election cycle.
The three networks were nearly 13 times more likely to be critical or challenging of conservative candidates' faith during the 2012 cycle, the MRC said.
Among its recommendations, the center said reporters should remember the 2012 elections likely will be decided on economic issues, not religious beliefs, and called for balance when reporting on matters of faith.