WASHINGTON (Reuters) - Social networking sites play a modest role in influencing most U.S. users' political views, with the biggest impact among Democrats, a survey showed on Tuesday.

The poll by the Pew Research Center's Internet & American Life Project comes as Democratic President Barack Obama and Republican challenger Mitt Romney are using Facebook Inc pages and other social media as campaign tools ahead of the November election.

"For most of those who use the sites, political material is just a small portion of what they post and what they read. And the impact of their use of the sites is modest, at best," Lee Rainie, director of the Pew project, said in a statement.

Thirty-six percent of social networking site users say they are "very important" or "somewhat important" to them in keeping up with political news, the survey showed.

The sites are "very important" or "somewhat important" to 26 percent of site users in recruiting people to get involved in political issues that matter to them.

A quarter of the site users say they are "very important" or "somewhat important" for discussing or debating political issues, the poll showed.

Twenty-five percent of users say the sites are "very important" or "somewhat important" in finding other people who share their views about important political issues.

In each case, Democrats are more likely than Republicans or independents to say the sites are important.

A third of Democrats and liberals who use social networking sites say their activities on the sites have led them to become more active, compared with 24 percent of site-using Republicans and independents.

The survey found that 84 percent of site users say they have posted little or nothing related to politics in their recent status updates, comments and links.

The telephone survey was conducted from January 20 to February 19 among 1,407 adults. The margin of error is plus or minus 2.9 percentage points.