WASHINGTON (Reuters) - Roughly a third of Americans view President Barack Obama more favorably and a third less favorably as a result of his declaration of support for gay marriage, a Reuters/Ipsos poll showed on Tuesday.Obama's announcement last week that he believes gay and lesbian couples should be able to wed stirred political passions, pleasing his Democrat base of supporters while upsetting conservative voters.While 40 percent of respondents in the online poll said the gay marriage decision had no impact on their view of the president, 31 percent said they saw Obama more favorably and 30 percent less favorably. Combined, the percentage figures add up to more than 100 because of rounding.Republicans and Democrats split clearly on the issue. Fifty-three percent of Democrats in the poll said they viewed Obama more favorably after his shift, while 56 percent of Republicans regarded him less favorably.(Reporting by Jeff Mason; Editing by Alistair Bell)