COLUMBIA, S.C. -- Texas Gov. George W. Bush holds a narrow three-point lead over Arizona Sen. John McCain among voters likely to participate in Saturday's crucial Republican primary in South Carolina, according to a Reuters poll published Wednesday.

The poll of 607 likely voters found Bush leading with 43 percent, over McCain with 40 percent and talk radio host Alan Keyes with 4 percent. The remaining 13 percent were undecided.

With the margin of error at plus or minus four percentage points, the race is a statistical dead heat.

The primary has become a crucial test in the battle for the Republican presidential nomination but the race is volatile because of the open primary system.

The poll was conducted Sunday and Monday by Zogby International. Reuters will publish new polls Thursday and Friday, each based on a two-day rolling sample of about 600 voters.

"This is obviously a horse race and too close to call right now," said pollster John Zogby. "McCain is heavily dependent on Democrats and independents while Bush has consolidated his hold among core Republican groups."

Within the poll sample, 62 percent were Republicans, 22 percent were independents and 16 percent were Democrats. The poll found rising interest in the primary among non-Republicans over the course of the two days of interviews.

Some 36 percent said this would be the first Republican primary in which they would participate while 29 percent said they had voted in past Democratic primaries and 28 percent said they voted for President Clinton when he was the Democratic nominee in the 1996 presidential election.

When they were asked which Republican had the best chance of winning the 2000 election, 54 percent said Bush and 37 percent said McCain.

Bush also had a higher favorability rating in the poll. He was rated positively by 81 percent and unfavorably by 15 percent. McCain's positive rating was 76 percent while 13 percent viewed him unfavorably.

The Texas governor has been hammering McCain over the air waves in the past two weeks as a deserter from traditional Republican beliefs in an effort to shore up support among the Republican base.

Illinois Republican Rep. Henry Hyde, a conservative who managed the impeachment trial against Clinton last year, recorded a message supporting Bush as the best candidate to oppose abortion. The message is being telephoned to 100,000 party faithful in South Carolina.