Democrat Barack Obama has built a 4-point lead over Republican rival John McCain in the race for the White House, aided by growing support from women and independent voters, according to a Reuters/C-SPAN/Zogby poll.

Obama led McCain 48 percent to 44 percent among likely US voters in the national poll, up from a 2 percentage-point advantage for Obama on Wednesday. The poll has a margin of error of 2.8 percentage points.

Obama expanded his advantage among independents to 13 points from 9 and his lead among women grew to 9 points from 7. The Illinois senator moved slightly ahead of McCain among Roman Catholic voters and now leads or is even with McCain in all age groups except those above age 70.

"Obama seems to be doing well among the groups that he really needs like women and independents," pollster John Zogby said. "McCain needs to do much better with them."    

McCain, a former Navy fighter pilot and Vietnam prisoner of war who has focused on security issues, was only running even with Obama among families with a member in the military.

"That is not a good sign for McCain," Zogby said.

The tracking poll, which will sample public opinion until the Nov. 4 election, was taken Monday through Wednesday. About one-third of the survey was conducted after Tuesday night's second debate, which featured sharp exchanges on the economic crisis.

McCain had hoped the debate could help him reshape a race that has been trending toward Obama, but Zogby said the one-day sample taken after the debate showed about a 6-point advantage for Obama.

"McCain did not help himself in the debate, that's pretty clear," he said. Obama has solidified his lead in most national polls in recent weeks as the Wall Street crisis focused attention on the economy, where polls show Obama's approach is favored by voters.

Independent Ralph Nader and Libertarian Bob Barr each registered support from 1 percent of respondents in the poll. Four percent of voters said they were still undecided.

The rolling tracking poll surveyed 1,203 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. -Reuters