ONE CLEAR WINNER emerged from the Iowa Republican forum Saturday night: the Republican Party. On the evidence before the nation's eyes, the GOP is awash with articulate, reasonable and attractive candidates for national office. No one of them scored a knockout punch over anyone else and there were no clear individual losers. But their collective performance made the party as a whole look good.

When candidates are faced with the prospect of 36 primary elections in just 14 weeks, "exposure" must be the objective of very campaign. For those who showed up in Des Moines, the exposure should prove to be helpful indeed. For Reps. Philip Crane and John Anderson and their underdog candidacies, a unique national platform was provided to define their differences with their better-known opponents. They capitalized on their opportunities. We must confess, however, to the suspicion that Rep. Anderson will win that unsolicited quadrennial designation as the Opposition Party's favorite candidate, much as Sen. Henry Jackson appeared to be the Democrat most acceptable to Republican voters in 1976.

Whether Mr. Reagan will come to regret his "regrets" won't be known until at least Jan. 21, the date of the Iowa delegate caucuses. He was, in fact, the target of more needles from the Republicans present than even President Carter. When former Texas governor John Connally exclaimed, "Oh, how I wish Gov. Reagan were here," the other candidates (with the notable exceptions of former ambassador George Bush and Sen. Bob Dole) hastened to deplore Mr. Reagan's absence and to put philosophical daylight between themselves and the acknowledged front-runner.

The principal causalty of the otherwise harmonious evening turned out to be Mr. Reagan's so-called 11th Commandment. That rule, which prohibits speaking ill of another Republican, was fractured in regard to Mr. Reagan by Mr. Connally, Sen. Baker, Rep. Anderson and even Rep. Crane, a former longtime supporter of Mr. Reagan. One can wonder if the restraint shown by Mr. Dole and Mr. Bush was motivated more by the hope of inheriting the Reagan constituency or by the dream of second place on a Reagan ticket next fall.

At times, the candidates were clearly ambivalent about which audience they were addressing: the nation or Iowa Republicans. This was most obvious on questions about President Carter's proposed grain embargo and on other agricultural matters. Provincial and partisan rhetoric prevailed in these two areas, with the singular exception of Mr. Anderson.

For all of the good feeling in Des Moines, the candidates did not distinguish themselves in answering a key question on how they might put into effect what has become the unofficial but near-unanimous 1980 Republican platform -- stop inflation, balance the budget, increase defense spending and cut taxes, all at the same time. The Republicans, at least on this one, seem to have learned something about rhetorical excess from the Democrats.

The "winners" and "losers" of Saturday Night Live in Des Moines will finally be determined by the decisions that voters in Iowa, New Hampshire and elsewhere make in their caucuses and primaries. Regardless, the entire program was worth the effort and must be helpful to Republican voters. Mr. Reagan was proved dead wrong about one of his professed reasons for not showing up: the forum was anything but "divisive. Rather, is showed -- surprise -- that Republicans can be fun.