TO THE FAMILIAR question of whether the government of Iran is really in charge in Tehran must be added the further question of whether it is acting, in the current negotiation, in good faith. Supposedly, careful and quiet arrangments had been made for a United Nation "commission of inquiry" to go to Tehran as part of a package that included early liberty for the 50 captive Americans. A dark cloud has been cast across that prospect, however, by Ayatollah Khomeini's latest bombshell. In a statement Saturday, he assigned to the still-to-be-elected parliament the decision on both the release of the hostages and the "consessions" to be obtained in return. Though the Khomeini statement did for the first time win the embassy militant's agreement to let someone other than themselves eventually decide the hostages' fate, it does seem to put off a resolution of the matter until April, and it is a very bitter pill.

Iran's United Nations ambassador, appearing on television yesterday, insistently denied that his government has broken a "commitment" or at least a "gentlemen's agreement." He had a weak case. Forget for the moment about the Carter administration, which, we belive, would not be lending itself to this sort of excercise in the first place unless it was expected to lead to certain results. Why would the whole United Nations apparatus swing into operation unless it were to resolve the affair in a timely fashion? Tehran in February in the midst of a struggling revolution and a full-fledged international crisis is not everyone's idea of a pleasant winter holiday. For the commission to arrive just in time to have the hostage-and-"concessions" issue broken off from its inquiry is a deep insult to the United Nations. The sequence can only make other countries, even ones sympathetic to Iran's purposes, ask if Iran is trifling with international good offices.

Fortunately, the commission at once started gearing up for its inquiry. It is not to excuse frustrations like this one to note that they were implicit from the outset once the United States gave up the idea of going after the hostages by force and decided instead to adopt a strategy of playing against Iran's volatile political process. Moreover, though it would convey the international community's dismay if the commission were to pack its bag and go home, the gesture would also indicate a certain acceptance of the new April-or-later timetable. That timetable is most certainly unacceptable. The seizure of the hostages, an outrage from the day it began, cannot be allowed to drag on and to be yielded as a political football to a legislative body that will have uncertain tendencies and powers and that has not even yet been constituted.

We are not optimistic. By staying and doing its work expeditiously, however, the United Nations panel just may be able to generate a more positive development of Iranian negotiating policy within the complex and still-shifting political scene in Tehran. The panel is, after all, giving Iran what it has long identified as its key priority: recognition that it has grievances that merit an internatinal investigation. For Iran to get what it most wants from the international community without giving what others (and not just the United States) most want -- a resolution of the overall crisis -- would be a travesty, and no self-respecting nation could go along with it.