COLUMBIA, S.C., MARCH 3 -- Vice President Bush holds a decisive lead over his three Republican rivals in this key southern state whose GOP contest Saturday will set the stage for the largest collective primary in the nation three days later.

A Washington Post survey of 1,000 people who say they will vote in the South Carolina Republican primary showed that Bush has the support of 49 percent, Sen. Robert J. Dole (R-Kan.) 26 percent, Pat Robertson 14 percent and Rep. Jack Kemp (R-N.Y.) 7 percent.

Robertson could challenge Dole for second place if turnout is low. Among those voters considered most likely to go to the polls -- they say they are certain to vote, they did vote in 1986 and they strongly support a specific candidate -- Bush's support rises to 55 percent and Robertson's to 17 percent. Dole support falls to 22 percent.

The poll suggests that Bush heads into next week's "Super Tuesday" voting in an especially strong position. A big victory in South Carolina could lay the groundwork for a strong showing across the South three days later. That would put the vice president in a commanding position to capture the Republican nomination as the campaign heads to Illinois the following week.

The findings are particularly ominous for Kemp. Leaders of his campaign have strongly urged him to drop out of the race for the GOP presidential nomination this weekend -- before Super Tuesday -- if he comes in fourth here.

The poll also suggests that Robertson faces the prospect of defeat in terrain that he considers very favorable to his drive to mobilize conservative evangelical Christians. About 65 percent of the prospective Republican voters here describe themselves as "born-again" Christians.

After he came in fourth in the New Hampshire primary last month, Robertson declared that he was "laying down the gauntlet" in South Carolina, a "do-or-die" state where "if I lose this one, I'm in trouble." This week, however, he has backed off, saying that South Carolina no longer is "a make-or-break state" and that "my staff has told me as I travel that they would like me just to hold a strong No. 2."

The Post poll was taken over six nights ending Wednesday. Despite the fact that South Carolina voters have been bombarded with appeals from all four Republican candidates, the rankings did not change over that time. That is an indication Bush's lead has been holding up under the assaults of his adversaries.

Many voters, however, make up their minds in the final days before a primary.

Banking on this possiblity, Dole, who had been running commericals only in the Greenville-Spartanburg market, tonight plunged heavily into the three other major markets in the state: Columbia, Florence and Charleston. The Dole ads are attacks on Bush's record on the Iran-contra scandal, textiles, taxes and the Intermediate-Range Nuclear Forces Treaty. In addition, Dole received considerable publicity from his endorsement today by Jeane J. Kirkpatrick, a former ambassador to the United Nations.

For his part, Robertson bought a half-hour of prime time television time tonight in every South Carolina media market and throughout the day urged voters to tune in.

In the broadcast, he took an aggressive, almost angry, stance. He said that negative feelings about him are caused by "anti-Christian, anti-southern bias" in the national news media and "distortions. . . from the other candidates."

Noting that President James A. Garfield had been a minister, Robertson said the central question is: "Does the fact that a candidate is, or has been, a minister prevent him from serving his country? I believe that the fair answer is no."

Robertson also offered an extended defense against the charge that he has made irresponsible statements. He said that idea stems from "incredible cases of distortion" by the media.

"This program can be the turning point for me, just like Jack Kennedy's speech was the turning point for his campaign when he addressed the Houston ministerial association," Robertson said earlier in the day, a reference to a speech Sen. John F. Kennedy gave in the 1960 campaign in which he dealt with his Roman Catholicism at a meeting of Protestant ministers.

Among the major findings in the Post poll:Former television evangelist Robertson is not the favorite candidate among any one of a number of categories of Christians. Among born-again voters, Bush gets 48 percent, Dole 21 percent and Robertson 20 percent. Among evangelicals, Robertson's support rises to 27 percent, still below Bush's 44 percent.

Even among Charismatic and Pentecostal Republicans -- groups providing much of Robertson's backing -- Robertson gets 32 percent to Bush's 47 percent.

Voters who say they watch television evangelists almost every week give Bush 44 percent to 27 percent for Robertson.

Robertson and his campaign strategists have argued that his high negative ratings among voters will fall as the campaign intensifies and the electorate learns that in addition to his televised evangelism, he is the well-educated son of a former U.S. senator and that he established a multimillion-dollar business at the Christian Broadcast Network.

This scenario has not panned out in South Carolina, where 59 percent of the Republican electorate views him unfavorably.

Campaign staffer Kerry Moody said Robertson's negatives stem partly from "the funny facts thing" -- Robertson's tendency to make strong assertions he can't substantiate -- and partly from voters' fear of putting a former preacher in the White House -- issues Robertson tried to deal with in his broadcast tonight.

The Robertson and Dole strategy of targeting rural sections of the state where Republican primary turnout traditionally has been low does not appear to be working. If successful, this strategy would give a candidate a chance to win delegates by carrying a plurality in rural congressional districts and to boost the statewide total. The poll indicates, however, that Bush's strength is roughly even throughout the state.

The core of Robertson's support is voters who place the highest priority on such moral and social issues as abortion, school prayer and drugs. About 83 percent of Robertson supporters said his stand on pornography is a major reason for their backing him, while only a third of the Bush, Kemp and Dole supporters identified this issue as a major factor in their decision. Robertson's stand on abortion is cited by 78 percent of his supporters as a big factor in the decision, twice the percentage of Bush supporters. About half of Robertson supporters cited the nation's "declining moral standards" or school prayer as the biggest reason for their support.

In terms of income, there are strong class differences between Bush and Robertson supporters, differences that provide modest support for the portrayal of the contest as one between the country-club wing of the GOP and the discount-store wing. About 59 percent of Bush supporters make more than $30,000 a year, and only 25 percent less than $20,000. In contrast, 44 percent of Robertson's backers make more than $30,000 while 37 percent make less than $20,000.

In one of the small ironies of the race, Dole, who has been seeking to portray Bush as a privileged member of a protected eastern elite, has a base of support that is equally as affluent -- if not sligntly more affluent -- as Bush's. And Dole backers are significantly better educated than Bush's or Robertson's.

South Carolina, where Democrats will vote March 12, is considered critical to the battle for the Republican presidential nomination for three reasons beyond its timing three days before Super Tuesday, when 17 states, most of them in the South, will hold GOP primaries or caucuses.

The contest is considered a test of the Bush "fire wall," the vice president's solid backing among his party's establishment throughout the South; it will be the first test of Robertson's Christian crusade in a state with a large percentage of born-again voters, and it is Kemp's last change to test whether his flagging attempt to mobilize the GOP's right wing can continue. Kemp, who has yet to perform well in a major test, has been advertising and campaigning heavily. Failure to do well would be a potentially fatal blow to his bid.

Polling analyst Kenneth E. John and political researcher Colette Rhoney contributed to this report.

-------------SOUTH CAROLINA REPUBLICAN PRIMARY VOTERS------------

Q. Which would you say is the single biggest reason why you supported your candidate?

................................. BUSH ......DOLE ......ROBERTSON

................................. SUPPORTERS SUPPORTERS SUPPORTERS

Keeping the nation's

..economy healthy................ 21%........26%........10%

Maintaining the nation's

..military strength.............. 20%.........9..........7

Federal budget deficit........... 12.........22..........3

Nuclear arms control.............. 6..........1..........1

Relations with

..the Soviet Union................ 5..........4..........0

Taxes............................. 4..........5..........3

The foreign trade

..imbalance....................... 3..........8..........1

Aid to the Nicaraguan

..contra rebels................... 5..........2..........1

Declining moral standards......... 3..........3.........33

Public school prayer.............. 2..........1.........14

Pornography....................... 0..........0..........3

Abortion.......................... 1..........2..........4

The drug problem.................. 4..........4..........4

Civil rights...................... 1..........1..........1

Other/None....................... 13.........12.........13

Results are from a Washington Post telephone poll of 1,000 Republican primary voters. Figures for Kemp voters are not shown. The margin of sampling error is plus or minus three percentage points. Sampling error is only one of many potential sources of error in this or any public opinion poll.