If you are terrified or appalled, as I am, by Ronald Reagan and his chances for the presidency, one question about him looms larger than the many others: How far can his emotional appeal carry him?

Until now, he has won votes because he has presented himself as the straight-talking cowboy quickest on the draw with sure-fire applause lines.

On Iran: "We should be so strong and so respected in the world that never again will some tinhorn dictator dare take over an American Embassy."

On big government: "I believe Americans want a crack at a decent job, a home, safety in the streets and a good education for our children; and the best way to have those things is for government to get out of the way while the rest of use make a bigger pie so that everybody can have a bigger slice."

On the Red menance: ". . . the Soviet Union is building the greatest war machine known to man. Somehow, we've negotiated agreements [under which] we grow weaker and they grow stronger."

As was said of John O'Hara, the novelist, it is easy to admire the man's style because his intelligence doesn't get in the way.

Except that Reagan is intelligent. He has the cunning to know that the current problems and confusions bedeviling America help to create odds that overwhelmingly favor the delivers of simplistic answers as against the raisers of complex questions.

Or at least that is how it worked during the Republican primaries, when serving up one-liners for the network news means more than laying out a dozen position papers on the press table.

If anything has changed, it is that coming into the Republican convention Reagan supporters were arguing that, sure, this guy has his share of rhetorical excesses, but beneath all the simplistic slogans he has plenty of substance.

That's to be doubted. If Reagan is really a man of depth, competence and integrity, where did it come from and how did he get it so suddenly? Little in the record of his pre-political years as a Hollywood actor or as a pitchman for General Electric suggests any sense of public service or idealism. Instead, these were merely the years of gelatinizing his biases that would later take shape in the endless speeches about the bumbling feds and the wicked Russians. s

In his acceptance speech to the Republican convention this week, Reagan has two choices: Give 'em more of the "tinhorn dictator" and "bigger slice of the pie" rhetoric and whip has his boosters into the kind of frenzy that the Right hadsn't felt since Barry Goldwater's slogans had it jumping in 1964. Or he can pose as the thoughtful moderate offering position-paper thoughtfulness about his vision for a new America.

Reagan, with his training as an actor, can be counted on to try for both roles. But he will risk the scrutiny of those who, after the convention, will go back and examine Reagan's performance, when as governor of California he was entrusted with power that was real.

Some of the scrutiny has already begun. When researchers for one of Ralph Nader's organizatioins examined Reagan's programs and decisions as governor, they found them "marked by groping, confusion, unforeseen consequences and occasional disdain for state and federal laws." In the six years since he left office, Reagan has been consistently trying to beautify his bleak record.

It ususally doesn't take much to uncover a Reagan distortion or deception. Morton Mintz, writing in the Sacramento Bee in June 1976, told of hearing Reagan say on national television that the Interstate Commerce Commission made "something like 42 trillion rate decisions" in its 85-year history ". . . and they are not even indexed." Mintz asked his son to check the figures on his $12.95 calculator. The 42 trillion decisions a year came out to more than 56 million an hour.

That, we are meant to believe by Reagan's managers, is just another of the old man's harmless flourishes. It's fine that the entourage sees through it all, but it's Reagan who's running for office. He's running blind, and proud of it.