NASHVILLE, Tenn. – Democrat Barack Obama has a narrow 3-point lead in the U.S. presidential race on Republican John McCain less than a month before the election, according to a Reuters/C-SPAN/Zogby poll released Tuesday.

Obama leads McCain among likely U.S. voters 48 percent to 45 percent in the national poll, which has a margin of error of 2.8 percentage points. Four percent of voters said they were still undecided.

The survey, the first in a series of daily tracking polls that will sample public opinion until the Nov. 4 election, showed Obama with an advantage among the crucial swing voting blocs of independents and women.

“Obama is leading among the key target groups, but this race is nowhere close to over,” pollster John Zogby said. “The deal is far from closed.”

The presidential rivals meet in the second of their three scheduled debates Tuesday in Nashville, Tennessee. The poll was taken Saturday through Monday, after the debate between vice presidential candidates Republican Sarah Palin and Democrat Joe Biden.

The poll found Obama led among independents by 49 percent to 42 percent and among women by 51 percent to 42 percent – two key swing groups that could decide a close presidential race.

The 47-year-old Illinois senator, who would be the first black U.S. president, won 9 of every 10 black voters in the poll and led among Hispanics, young voters, self-described moderates and those making less than $50,000 a year.

McCain, 72, an Arizona senator, led among men, whites, older voters, Catholics, and those making more than $100,000 a year.

Each candidate has solidified support in their own party, the poll found, earning nearly 9 of every 10 members.

Strong voter registration efforts launched by Obama and Democrats appeared to pay off, with Obama leading McCain by 63 percent to 47 percent among voters who have registered to vote in the last six months.

But the bruising nature of the campaign has taken a toll on both candidates, who registered favorable scores from barely more than 50 percent of the voters in the survey. McCain was rated favorably by 57 percent, while Obama was rated favorably by 55 percent.

Independent Ralph Nader and Libertarian Bob Barr each registered support from 1 percent of respondents in the poll.

The rolling tracking poll surveyed 1,237 likely voters in the presidential election. In a tracking poll, the most recent day's results are added while the oldest day's results are dropped in an effort to track changing momentum.

(Editing by Mohammad Zargham)