IT IS in the week before their national convention officially begins that the Republicans, Lord love their excesses, traditionally do whatever kookywork they have in mind for that year's show. The Democrats do it differently: with their unfailing instinct for providing absolutely gripping, fratricidal warfare on prime-time TV, they tend to build toward explosion as the main event. Their fights generally get worse as the proceedings wear on, whereas those of the Republicans generally get buried.

Connoisseurs of the four-yearly GOP follies will remember nostalgically in this connection, for instance, the wonderful platform plank of 1976 in which the Grand Old Party called for repeal of the basic federal aid to education statute, the funds to support public schools to be provided instead from tobacco taxes. Speculating on how it would work became, if only briefly, the rage at Kansas City, the basic scenario being one in which a ravaged, emphysemiac nation coughed, hacked, gasped, spluttered and choked its way closer to death each year in order to move its 9-year-olds from 4a to 5b.

That plank, as all remember, got sawed off. Things looked up. But that doesn't seem to be the way things are going to turn out in Detroit in 1980. Too bad: 40 years is a kind of long time for a party to have supported the equal rights amendment only to drop it now, especially when the prospective candidate, Mr. Reagan, was ready to go a way farther to accommodate party traditions on this, not to mention the strong pro-ERA feeling and commitment of many Republicans. The Republicans have been including a plug for ERA in their platform every four years since Phyllis Schlafly was a mere girl of 15. Surely in a logical and consistent world, their conservatism if nothing else should have required more of them to be leery of this sudden change. The next thing you know they'll be coming out for "progress."

If we don't show a proper degree of distress about this turn of events or even register much more than a pro forma complaint about the platform committee's ill-advised support for those seeking a constitutional ban on abortions, it's because we don't think the issues involved in these planks are going to be all that much affected by what the platform drafters in Detroit dream up or re-endorse for this year. What will be affected is the fortune of the Republican Party.

It is a terrible conceit of people who are not card-carrying members of the Republican Party to advise its minions, every four years, through an expression of heavily burdened, lugubrious sincerity, what it is in their own "best interest" to do. So we will try to be brief and uncomplicated about it. The Republicans stand a pretty good chance of transforming themselves this year into a winning party. Their candidate has a large opportunity. They are, even now, in the process of defining themselves -- and doing so in public view. This year they seem felicitously free of left-right struggle within the ranks. No one is asking them to abandon their fundamental dogma -- their conservatism -- in order either to get with it or, expediently, to win.

They can, in other words, conceivably have the whole thing this year. But that will probably depend on the capacity of their dominant right wing to resist the temptation to have it all their way, and to avoid the pitfall of writing themselves and their party into an ever tighter, tinier place, an ideological staging ground from which to drive away would-be allies and all but the doctrinally super-pure. Phase One of the platform proceedings has that unhappy look.