WITH THE Republicans -- never mind how moving and powerful their speeches may finally be -- it is always, at some point, the land of Oz. Somehow late Wednesday night as Ronald Reagan stood on the podium in Detroit informing the convention that it would be George Bush after all, we looked at the assemblage and saw only Dorothy -- back home, safe in Kansas, with a story of where she'd been that day and what had happened there and whom she'd met that Aunt Em was never going to believe.

In fact, the twister that blew the convention temporarily out of reality on Wednesday was pretty unbelievable in mere political terms. Elevator-diplomacy, as we have come to think of this latest improvement on the shuttle, created and evidently carried fairly far along an absolutely preposterous negotiation between former governor Reagan and former president Ford. By early evening the gag line making the rounds at the convention was that Gov. Reagan was likely to be allowed to "keep OSHA," while all other responsbility would devolve on his vice president.

We doubt the thing was as batty as that, but its conception was surely batty.

Could Mr. Reagan really have intended to make such a grant of power as was being discussed to a vice president (or anyone else)? Could Mr. Ford really have believed that any assurances given, in writing or not, or even sworn in blood, would have had any standing whatever or could not have been revoked by a president whenever he chose? Surely the best thing about the bizarre proposition was that it never got any farther than it did.

But that it got anywhere at all says something perplexing about Mr. Reagan's own conception of the office he is seeking. With Mr. Bush, he reached an orthodox and understandable result. But the terrain he seems to have negotiated to get there was truly the long way around, and much more will be said about the meaning of this strange journey in the next few days than about the fellow he has finally asked to be his running mate. The question, unthought of until now (there was no reason to think of it), is whether Mr. Reagan could be content to take a regal head-of-state view of the office, it he is elected, and subcontract out the work to someone else. The Ford adventure, unfortuantely for him, gives Mr. Reagan something else to explain.

It tells you more about the convention than the vice presidential candidate to observe that in the context of Detroit '80 politics the anxiety of the dissenters was that George Bush was "too liberal" for the Reagan supporters. Here is a rule of thumb you can invoke with confidence: anyone who thinks Mr. Bush is a liberal is not one himself. George Bush does not exactly pose a huge danger to the republic from the left. He is rather a center-right, traditionalist, establishment-oriented competent government figure who showed himself to be resilient but not especially presidential in the campaign he ran in the past couple of years. His selection by Gov. Reagan in preference to others who were more closely identified with Mr. Reagan's own political views and style suggests that the former California governor is serious about winning and has made what is probably politically the most reasonable choice. Mr. Bush, in addition to his other politically appealing attributes, comes equipped with a tested campaign organizer.

But the political value too is contingent. It is contingent upon Mr. Bush's own performance in the drawnout campaign proceedings that lie ahead. George Bush's resume is right in every respect. And in private, one on one, he is known to be an impressive person. As a public campaigner over the past couple of years, he left much to be desired and seemed often to convey exasperation rather than power or force in his stump exhortations. Maybe that will change. The Republicans this year have an enormous opportunity. They may have the right ticket to take advantage of it. Mr. Reagan's remarkable acceptance speech last night was one sign anyway that they will make a serious try.