Ronald Reagan came to the Republican convention as an actor trying out for the part of Mr. President. He left with a grave sense of the deadly serious business he was getting into.

So while the failure to win President Ford to the ticket looks bad, the effort served the candidate and the country. Especially since George Bush makes a good running mate.

Two factors gained the presidential nomination for Reagan. First, there was the tide of history -- the gathering of the overwhelming majority of the Republican Party, and a considerable fraction of the country, around the conservative banner taken over by Reagan after 1964.

Joined to that was a warm, unthreatening personality that resisted, and even turned to account, the bogeyman charges usually leveled against conservatives. It is typical that Reagan forged to the fore in the primaries when he made a firm, but humorous, response to a harsh question about ethnic jokes in the first New Hampshire debate.

Along with those qualities came weaknesses so abundant as to make every bone in Reagan's body seem a glass jaw. Apart from age and inexperience in national and international affairs, there was the sophomoric approach of right-wing populism.

Reagan spoke of the most baffling problems in the language of T-shirts and bumper stickers. He tossed big numbers around like Frisbees. Ignorance regarding such common counters of public business as agricultural parity or U.N. Resolution No. 242 bothered him not at all. He talked of being president, in the laid-back California style, as if it were truly possible to serve in the White House as "chairman of the board."

The choice of a running mate, because of these weaknesses, was crucial for Reagan. He needed someone who would strike the country immediately as presidential. That indicated a well-known figure with experience in national and international affairs and with an appeal to moderate Republicans and middle-of-the-road Democrats in the "battleground" states of the Northeast and Middle West.

Ford was ideal. He had been president. He united all factions of the Republican Party. He was especially strong in such states as Michigan, Illinois and New Jersey.

So Reagan's decision to go for Ford, despite differences of position and an unhappy history in personal relations, speaks well for his judgement, in general, and his willingness to be pragmatic, in particular. Had the negotiations borne fruit, Reagan and his people would have been hailed for political genius.

As I understand it, the effort to parcel out presidential authority proceeded resonably smoothly. What went wrong was the personal chemistry. Ford came to feel that he was under pressure, and reacted by blabbling all over town -- in his usual inadvertent, on-purpose way -- about his insistence on a "meaningful role" in a "co-presidency." Reagan resented the talk, and began pressing for an immediate answer. Ford balked at what he considered an ultimatum. Reagan than called off the negotiations and turned to Bush.

The spectacle of Reagan running after Ford and failing to get him will no doubt work against the Republican candidate. The Democrats can scream that, besides being inept, Reagan played fast and loose with the Constitution. But otherwise the episode is not so damaging.

George Bush, to be sure, comes off looking like a distinct second-best. But Bush has done a wide variety of different jobs well. He commands respect and affection in important sections of the Republican Party. He knows the issues and he knows the country. He is dead loyal -- a true team player. I think that as a vice presidential candidate he will do exactly what he had done in all his previous posts -- namely, far better than expected.

The true bonus, however, is what the convention experience does to Reagan. He now knows, as he never knew, that there are decisions only the president can make. He knows those decisions engage substance and details -- not just appearance and tone. He realizes how much the clock runs on a president, and that the decision-making process is a real thing, not just a busswork. The experience of the convention, in short, has caused Reagan to sober up.

His acceptance speech reflected at least some of the change. It was sober in tone, and positively reached for a sense of history. There was no glib talk about achieving "military superiority" or cutting billions from the budget. An effort was made to undo silly things said about women's rights and Social Security. The emphasis -- particularly in the reference to an American Compact -- was on unity. The call for a moment of "silent prayer" struck home.

That is probably the best that can be expected this year. For at bottom, the fight between Reagan and Jimmy Carter comes down to a competition as to which of the two unlikely prospects is the least unqualified to be president.