The United States has been pressing for a long time for the bombing of Serbian ammunitions depots, rather than the targets of scant military significance selected by United Nations commanders and NATO in previous raids.

The NATO air raid today, the first since last November, thus bore the hallmark of American planning and prompted a ringing chorus of support from Mr. Clinton and Defense Secretary William J. Perry. It underscored the current United States policy of engaging in diplomatic talks with the Serbian leadership in Belgrade while trying to weaken and isolate the Bosnian Serbs in Pale.

The attack also confirms that the United Nations, faced with the choice of taking a tougher stance or withdrawing from Bosnia, has opted for now for the former course.

In February 1994, a NATO ultimatum established a zone radiating 12.5 miles around Sarajevo from which all heavy weapons were banned. But that "exclusion zone" has steadily eroded to the point where Sarajevo once again lives in terror and isolation, subjected to regular shelling that has killed dozens of people this month and pushed weary civilians off the street.

Lieut. Gen. Rupert Smith, the British commander of United Nations forces in Bosnia, requested the air raid today after Serbs failed to return four guns taken in recent days from United Nations weapons-collection points. The Serbs had been given until noon local time to give back the weapons.

A further ultimatum from General Smith requires the Serbs and Bosnian Government forces to hand over or remove all heavy weapons within the 12.5-miles radius of the city by noon Friday.

In the past, tensions between NATO and the United Nations over when and how to bomb have bedeviled relations between the organizations. The United Nations has generally been reluctant to countenance strong action because of the vulnerability of its soldiers on the ground. But in the face of the recent crumbling of the United Nations mission, those difficulties appear for the moment to have been overcome.