WASHINGTON, July 29, 2008 (AFP) - White House hopeful Barack Obama's foreign tour has had only a muted impact among voters, and many Americans believe the Democrat is getting over-the-top media coverage, Gallup said Tuesday.

In the first in-depth look at public perceptions of the Democrat's trip to Afghanistan, Iraq, the Middle East and Europe, the survey organization said 35 percent of respondents had a positive opinion of last week's tour.

But 26 percent had a negative opinion and 39 percent said they did not know enough about the trip to be able to say, despite blanket coverage including overseas interviews with Obama by all the main television networks.

Gallup said its findings suggested that vitriolic attacks on Obama by Republican contender John McCain, including about the Democrat's failure to visit wounded US troops in Germany, may have had an impact.

'The heavy coverage of the trip may have fueled speculation -- or reinforced pre-existing attitudes -- about news media bias in Obama's favor,' Gallup added in its poll, conducted with USA Today.

The number of respondents who saw press coverage of Obama as unfairly positive was 39 percent. A total of 32 percent said coverage of McCain was unfairly negative.

'The media's coverage of Obama's foreign trip, coupled with a strong reaction from McCain and other conservatives, may have created the seemingly paradoxical effect of increasing Republicans' energy and excitement about voting for McCain,' Gallup said.

'If this is the case, the degree to which this is short-term versus long-term is still not clear.'

Obama's favorable rating dropped from 64 percent last month to 61 percent in the new poll. McCain's had increased from 59 percent to 62.

Overall, the Democrat leads his Republican rival in Gallup and other polls by a margin of about three points, according to an average by RealClearPolitics.com.