WASHINGTON (Reuters) - Voters say President Barack Obama did a better job than Republican Mitt Romney in Monday's debate but their opinions of each candidate did not shift significantly, according to Reuters/Ipsos poll released on Tuesday.

Some 47 percent of registered voters surveyed in the online poll judged Obama the victor, while 31 percent believed Romney won.

But neither candidate's favorably ratings shifted in the wake of Monday's debate, the last of three televised matchups before the November 6 election. Likewise, voter assessments of the candidates on a range of issues from the economy to foreign policy did not change by a statistically significant margin.

The full impact of the debate on the race won't show up in opinion polls for several more days, but it is unlikely that it will give either candidate a big enough boost to break their statistical tie, Ipsos pollster Julia Clark said.

"By this point in the election cycle a lot of people have formed a more complete view of each candidate," Clark said.

The accuracy of Reuters/Ipsos online polls are measured using a credibility interval. The survey of 515 registered voters, conducted on Tuesday following the debate, has a credibility interval of 4.9 percentage points.

(Reporting by Andy Sullivan; Editing by Alistair Bell and Doina Chiacu)