Washington, Oct 9 (IANS): Last week's first presidential debate in which Republican presidential challenger Mitt Romney bested President Obama by most accounts has given him a boost, according to two new national polls.

According to a Pew Research Centre survey conducted Oct 4-7, four days after last Wednesday's first presidential debate in Denver, Colorado, 49 percent of likely voters say they back Romney, with 45 percent supporting Obama.

In Pew's previous poll, conducted in mid-September, the president had a 51 percent-43 percent lead among likely voters.

Among registered voters, Obama and Romney were both at 46 percent in the Pew survey released Monday. In mid-September Obama was at 51 percent and Romney was at 42 percent among registered voters.

Meanwhile, Gallup's latest daily tracking poll of registered voters, also released Monday afternoon, indicates the president with a 50 percent-45 percent advantage over Romney. The president's edge is within the survey's sampling error. The poll was conducted Oct 1-7, both before and after the debate.

Responding to the Pew poll, an Obama campaign official cited by CNN pointed to a shift in the party identification percentages used in Pew's mid-September poll compared to the poll released Monday.

The earlier survey was composed of 39 percent Democrats, 29 percent Republicans and 30 percent independents, while Monday's poll was comprised of 31 percent Democrats, 36 percent Republicans and 30 percent independents.

Another Obama campaign representative cited by CNN said the "state of the race is what it has been, which is a close and competitive race in key states with a slight lean towards the president."

Meanwhile, a Romney campaign official said the Republican effort was "encouraged by the enthusiasm we are seeing from supporters who are energized, as well as undecided voters who are now giving the Governor a new look."

They are "continuing to work hard to bring home persuadable voters," the official said.