WHAT SOME people in the Reagan administration wanted from the firing of Eugene Rostow as arms control director was, among other things, more orderliness in the bureaucracy: Mr. Rostow had been regarded as a loose cannon. What they got instead was a surge of public turbulence so strong that the president himself was forced to assert (and by asserting to call into further question) that he was in control.

The story got highly romanticized, and that added to the pressure on Mr. Reagan. Mr. Rostow was portrayed as a conscientious arms-controller who had strayed beyond his instructions at the INF talks at Geneva, explored a Euromissile compromise and been fired for his pains. Actually, Mr. Rostow had announced the pursuit of such a compromise, and Moscow's rejection of it, last December. But only in the excitement of his ouster did the sequence come to be widely presented--here and in Europe--as evidence of his superiors' indifference to arms control and his own passionate commitment to it.

Was or is this impression fair? Regardless of how the administration's commanding echelon felt earlier about abandoning Mr. Reagan's opening "zero option" position at INF, the pressure for an acceptable compromise is growing. Having let Mr. Rostow go, Mr. Reagan accepted at his last news conference a challenge to renew confidence in Mr. Rostow's comrade-in-arms-control, INF negotiator Paul Nitze. Wisely, he skirted an invitation to reaffirm the zero-option-or-nothing position, saying that he would not get publicly into the "tactics of negotiating." Meanwhile, the Rostow departure opens wider the bureaucratic space available to Secretary of State George Shultz, and strengthens the demand for his contribution and direction.

Andrei Gromyko has been in Germany trying to frighten the allies into accepting the Andropov Euromissile proposals. Vice President George Bush heads to Europe shortly to . . . well, to what? There is an unseemly aspect to this competition for the confidence of a Europe apparently so fickle it has trouble deciding whether the greater danger comes from its enemy or its ally. It began, after all, as an American effort to satisfy the Europeans' request for greater protection against a burgeoning Soviet missile threat. Now Washington is asked to prove it is worthy of protecting them.

The task, however, must be done. Driven by its own demons, the administration has held until now that to make deterrence work it must project to the Soviets a readiness to fight a nuclear war if necessary. Therein lies Mr. Reagan's giant contribution to the European peace movement. Mr. Bush's trip is the right occasion --perhaps the last--to get back to an unadorned, public, credible commitment to the deterrence of nuclear war. There lies the way to get a Euromissile agreement worth having, and to lead the alliance.