Vice President George Bush holds a strong lead over rival Bob Dole among likely GOP voters in South Carolina's primary, according to a poll published today. The Washington Post said Bush had the support of 49 percent of 1,000 people who said they would vote in the GOP primary, while Dole had 26 percent, Pat Robertson garnered 14 percent and New York Rep. Jack Kemp claimed 7 percent. Among those voters most likely to go to the polls _ those who said they were certain to vote, had voted in 1986 and strongly supported a specific candidate _ Bush had 55 percent support to Dole's 22 percent and Robertson's 17 percent. Figures for Kemp were not provided in that category. The Post survey, taken over six nights ending Wednesday, had a margin of error of plus or minus three percentage points. The South Carolina contest takes place just three days before the big round of Super Tuesday primaries and caucuses concentrated in the South. The Post survey found that even among several different categories of Christians, former television evangelist Robertson was not the favorite. Among voters who said they watch television evangelists almost every week, Bush got 44 percent to Robertson's 27 percent. The core of Robertson's support, according to the poll, was among voters who placed high priority on moral and social issues. About 83 percent of Robertson's backers said their main reason for supporting him was his stand on pornography. Robertson's stand on abortion was cited by 78 percent of his supporters as a big factor. About half cited concerns about ``declining moral standards'' or school prayer as the biggest reason for their support.