NORTH CHARLESTON, S.C., FEB. 28 -- From his pulpit at the Northwood Assembly of God, the Rev. Fred Richard roared his warning that "you are engaged in spiritual warfare. It is a war between heaven and hell."

The church itself, he shouted, is "still under violent assault," as "we have taken Christ out of our prayers in schools, we have eliminated and murdered thousands of our babies every year."

As Richard ministered to his packed congregation of more than 750 men and women, campaign workers for Pat Robertson roamed the parking lot, placing on each car a letter from the former television evangelist:

"If you saw someone about to kill a baby, would you stop them? Of course you would! But more than 100,000 unborn babies are murdered each month . . . . This nation is facing a great moral crisis."

The letter asked for votes, and all indications are that Northwood Assembly and other evangelical, charismatic churches will turn out for Robertson in the South Carolina GOP primary on March 5, three days before "Super Tuesday."

For Robertson, Vice President Bush and Rep. Jack Kemp (R-N.Y.), South Carolina has become critical. The candidate with the most at stake is Robertson, who has thrown down the gauntlet in his southern "back yard," although the odds here are running against him.

On Saturday, the collective decision of the voters will be the first test of the strength of Bush's southern "fire wall" and perhaps the most decisive test of the muscle of the Christian-evangelical political movement, initially mobilized by President Reagan and now the core of support for Robertson.

South Carolina has become, in effect, the preliminary bout ahead of 17 other states, most in the South or on the border, that will hold GOP primaries or caucuses March 8. The South Carolina results are expected to influence the outcome of Super Tuesday.

By any standard, Bush goes into the South Carolina contest with a decided advantage. Not only do Reagan's high favorability ratings among Republicans reflect on his candidacy, but he also has the support of the state's GOP establishment, including Gov. Carroll A. Campbell Jr.

These advantages were apparent in a poll published today in The State, Columbia's newspaper. Conducted last Monday through Wednesday, the survey found that 48 percent of the respondents supported Bush, 25 percent backed Sen. Robert J. Dole (R-Kan.), 19 percent were in Robertson's corner and only 3 percent said they would vote for Kemp.

There are two wild cards in this contest. The most important is the true strength of Robertson's support. Polls in other states have occasionally underestimated Robertson, and officials in the Bush and Dole camps assume that the Robertson figures are low. If that is the case, Robertson, who is likely to benefit from the fact that Democrats are free to vote in the Republican primary here, could be a serious contender despite his 19 percent showing.

The second unknown is Dole. He won the endorsement of South Carolina's popular Sen. Strom Thurmond (R), but has bought television time in only one of three major markets in the state, Greenville-Spartanburg.

Dole aides say they remain undecided whether they will spend money in Columbia and Charleston, and they have yet to use commercials attacking Bush for his opposition to legislation protecting the textile industry -- a stand that could seriously hurt the vice president if it becomes a major issue. Bush aides are primarily worried that Dole will use old film showing Bush making an offhand remark -- "C'est la vie" -- to explain that he and Campbell differ over the textile bill.

A full-scale Dole campaign, according to many observers here, would eat into Bush support, further increasing the likelihood of a Robertson win. Dole and Robertson have been moving up in the polls while Bush has fallen, and it is possible that Dole could make a serious challenge, although he has a poor organization and has not set the early groundwork for an intense campaign.

The critical importance of South Carolina was reflected in the GOP debate today in Atlanta, where Dole and Robertson stressed their support of the textile bill, while Bush and Kemp opposed it.

University of South Carolina political scientist Earl Black, who helped The State analyze the poll results, said the contest between Bush and Robertson is a "fight between the educated new middle class and the relatively uneducated lower-middle class and working class, the group that has been moving out of the Democratic Party into the Republican primary process."

He noted that "one of the real ironies of this contest" is that a key engineer of the Reagan mobilization of the Christian evangelical movement was Lee Atwater, a South Carolinian now managing Bush's campaign.

As the race here has grown more heated, Robertson has made a number of controversial remarks that may help him build turnout among his core constituents, but that also may hurt his bid to expand his base into the regular wing of the GOP. Robertson has suggested that the Bush campaign orchestrated the leak of information about television evangelist Jimmy Swaggart to damage the Robertson drive, and he said the staff of Christian Broadcasting Network knew the whereabouts of hostages in Lebanon, a claim he has since backed away from.

Kemp has been campaigning and spending heavily here, but his effort has not been mirrored in the polls. In The State poll, he fell from 5 percent to 3 percent over two months.