WASHINGTON (Reuters) - Democrat Barack Obama’s lead over Republican rival John McCain held steady at 7 points as the race for the White House entered its final four days, according to a Reuters/C-SPAN/Zogby poll released on Friday.

Obama leads McCain by 50 percent to 43 percent among likely voters in the three-day national tracking poll, virtually unchanged from Thursday. The telephone poll has a margin of error of 2.9 percentage points.

“Essentially there is no difference in today’s tracking,” pollster John Zogby said. “Obama is holding firm and McCain is not making any gains.”

It was the second consecutive day Obama’s support has hit the 50 percent mark, and the eighth day out of the last 11. McCain’s support has not surpassed 45 percent in more than three weeks of polling.

The Illinois senator held steady among several crucial blocs of swing voters in the Nov. 4 election, leading by 15 points among independents, 9 points among women, 5 points among men and 9 points among Catholics.

Obama led in every age group and among every income group except voters who make more than $100,000. McCain, a former Navy fighter pilot and Vietnam prisoner of war, trails among voters with a member of the military in their family.

Mccain, an Arizona senator, also was winning only 26 percent of Hispanics, a fast-growing group that gave Republican President George W. Bush more than 40 percent of their vote in 2004.

“If you are John McCain you want to see something start changing in this race, and right now it is not,” Zogby said.

Obama has led McCain in every national opinion poll for weeks, and McCain also trails in many of the key battleground states including Ohio, Florida and Pennsylvania.

McCain was on a bus tour of Ohio and Obama was in Florida, Virginia and Missouri on Thursday, trying to drum up turnout and win over undecided voters in some of about a dozen states that will decide the race.

Independent Ralph Nader received 2 percent in the national survey, and Libertarian Bob Barr was at 1 percent. About 2 percent of voters remain undecided.

The rolling tracking poll, taken Tuesday through Thursday, surveyed 1,201 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 to monitor changing momentum.

The U.S. president is determined by who wins the Electoral College, which has 538 members apportioned by population in each state and the District of Columbia. Electoral votes are allotted on a winner-take-all basis in all but two states, which divide them by congressional district.