WASHINGTON -- Democrat Al Gore continued to hold a slight lead over Republican George W. Bush in the Reuters/MSNBC daily tracking poll released Thursday, the first to reflect some impact of Tuesday's presidential debate.

The survey also showed what pollster John Zogby called a "surge" of support for Green Party candidate Ralph Nader, which could affect the neck-and-neck presidential race in battleground states.

The poll, conducted by Zogby, surveyed 1,209 likely voters between Monday and Wednesday. It found the vice president leading the Texas governor 46 percent to 40 percent, five weeks ahead of the Nov. 7 election. Bush dropped a point from Wednesday's poll while Gore remained steady.

"Again this race is very close -- close among voters over 50, close among voters earning more than $50,000, close among suburban voters and those who have had some college or a college degree," he said.

Nader, the third party candidate who was excluded from the presidential debate in Boston, rose two points to 7 percent in the new survey.

"Gore holds on to his lead, but Nader has picked up significant support, especially after the debate," Zogby said.

Nader was up to 17 percent among independents and 18 percent among progressives.

"If he continues the same trend, he will have an impact on several of the battleground states," Zogby said.

The Reform Party's Pat Buchanan had 1 percent of the likely voters polled, while Libertarian candidate Harry Browne and Natural Law's John Hagelin had less than 1 percent.

Another 7 percent were undecided.

POLL SHOWS DEBATE IMPACT

Reuters and MSNBC will release a new poll every day until the election. The surveys are made up of a rolling daily sample of 400 likely voters each day to create a three-day sample of about 1,200. The race is now on the outer edge of the statistical margin of error of plus or minus 3 percentage points.

The effect of Tuesday's presidential debate began to be reflected in Thursday's poll and will be further revealed over the next two days.

Of the 400 calls made Wednesday after the debate, Gore led Bush by 46 percent to 39 percent while Nader posted 7 percent of the voters.

There has been little movement in the poll since it began last Friday. Gore has moved in a narrow 44-46 percent range while Bush has moved in an only slightly wider range of 40-44 percent.

The two vice presidential candidates, Democrat Joseph Lieberman and Republican Dick Cheney, hold their only debate Thursday night in Danville, Kentucky.

Past vice presidential debates have produced some memorable moments but rarely had much effect on elections. But with Gore holding only a wafer-thin lead over Bush, even a small movement in the polls could be crucial.

While Gore maintains a lead among 18- to 29-year-old voters (49 percent to 31 percent) and among 30- to 49-year-old voters (46 percent to 37 percent), the two major party candidates are tied among 50- to- 64-year-olds and voters over 65.

One of the campaign's major issues has been health care for seniors, particularly access to affordable prescription drugs.

GORE HAS BIG LEAD AMONG YOUNG

Gore's 20 point lead over Bush in the 18-to 24-year-old age group could be a signal. That group has voted for the winning candidate in every race since 1972, Zogby said.

Gore and Bush are virtually tied among men (Gore 43 percent; Bush 41 percent) but Gore, who made a strong defense of abortion rights in the debate, continues to lead among women, 49 percent to 38 percent.

Bush's biggest leads continue to be among Christian conservatives and rural voters. Bush also leads among whites, while Gore still leads among African-Americans and Hispanics by wide margins.

In the presidential race, 81 percent of likely voters polled said they were unlikely to change their vote before the Nov. 7 election.

Seventy-two percent -- up from 68 percent in the previous poll -- said they had definitely ruled out voting for Bush while 73 percent said the same about Gore, compared to 74 percent in the earlier survey.