COLUMBIA, S.C. -- The smile was warm and the tone soft and unhurried, but Pat Robertson's words dropped like hammer blows when he accused George Bush's campaign last Tuesday of such ridiculous political crimes that Robertson's supporters were worried.

''I'm almost afraid to open the papers anymore,'' Carole Wells, the hard-driving Robertson coordinator in Spartanburg County and highly respected state legislator, told usover coffee shortly after Robert-son's diatribe against the vice president. Another Robertson insider agreed: ''It isn't the way I'd run a campaign.''

Why, then, did Robertson explode at Bush? The answer goes to the heart of what ails the preacher-turned-politician. Unlike the words that poured forth from his old CBN television pulpit, completely free of scrutiny by the press, every word issuing from his mouth as a presidential candidate gets instant analysis from the media, his political adversaries and his critics.

Because it is late for Robertson to be learning the cost of his poisoned arrows, that cost could be high. The charismatic evangelicals, for sure, are going to remain his -- heart and soul -- no matter how irresponsible he is. But they are not his target. His target is what one state party leader calls the ''larger sphere'' of the real Republican world, out there far beyond the evangelical base. Failure to penetrate that world -- and the crossover world of conservative Democrats -- means failure for Pat Robertson.

He got almost 50,000 signatures on his petition drive last year, most of them evangelicals. But if the turnout in the March 5 primary, three days before Super Tuesday, reaches the record 165,000 to 200,000 expected, the necessity for his broadening that base is urgent, to say the least. Without attracting conservative Republicans, Robertson cannot possibly do better than a strong second to the vice president in the state that gives him his best chance anywhere.

The well-worn Robertson bludgeon, first employed against Rep. Jack Kemp in Iowa and New Hampshire, was ineffective when Robertson turned it on Bush. No attack based simply on innuendo could make the case of conspiracy in the timing of the Swaggart scandal or succeed in charging ''dirty tricks.'' Nor has Robertson given even faint proof that Bush has a secret strategy to use ''religious bigotry'' against him.

Such campaign tactics infuse the candidate with a certain weirdness, making it far more difficult to get himself perceived as a trusted, bona fide future president. They frighten and turn away the very mainstream Republicans Robertson desperately needs.

Robertson can rightly say that he was the victim of heavy political infighting when Kemp switched sides in Michigan, and that party regulars tried to put off the Hawaii precinct caucuses when they realized Robertson's strength. But if he regards his charges against Bush as acceptable retaliation, he exposes himself as politically ignorant and even silly.

He made similar trouble for himself when he retooled a speech prepared for Sen. Jesse Helms that made a strong case for on-site inspection of possible offensive missiles in Cuba. His conversion of that carefully researched speech into a charge that SS-4s and SS-5s are now in Cuba made him a laughingstock.

In his more coherent periods, Robertson's political message is aimed at elevating his candidacy over his evangelical base. Before a crowd that almost filled the ballroom of the Executive Suites hotel here last Monday evening, school prayer, drugs, abortion and family issues came last. His major theme was nationalistic and patriotic. He warned of new dangers from ''global communism,'' attacked the INF missile treaty and denounced Reagan administration policies that, he said, have greatly increased textile imports from Communist China and the Soviet Union.

The crowd roared approval when he spoke the most protectionist line heard from any Republican presidential candidate: ''I am not going to let American workers lose their jobs so that Communist Russia and Communist China can have a prosperous economy.''

Talking up the big dramatic issues of foreign policy and national security makes sense for the former pulpit pastor. ''That's what he needs,'' one Robertson aide told us. ''It puts him closer to the mainstream.''

But he has not come into the mainstream yet, and if he does not master his tongue he will be moved farther away.