RIYADH, SAUDI ARABIA, FEB. 3 -- U.S. command of the skies over southern and western Iraq has allowed allied pilots to bring their firepower to bear on Iraqi Scud missile launchers more quickly and effectively than in the earlier stages of the fighting, U.S. military officers said today.

Allied air supremacy, which Gen. H. Norman Schwarzkopf formally claimed Wednesday, has meant fighter aircraft can for the first time safely patrol over Iraq with little fear of opposition from air defenses. This includes the nighttime hours when Iraqi technicians have been firing the Scud missiles. Fighters are poised to attack Scud launchers as soon as AWACS flying radar platforms or other surveillance aircraft detect a launch.

Previously, U.S. aircraft could be called in from more distant points once a missile was detected, but the mobile launchers often were gone by the time the attack planes got to the site. The cloud cover that settled over the region early in the war also helped shroud Iraqi getaways, generating a pattern in which more Scud firings occurred on cloudy nights.

In a demonstration that the new tactics work, the U.S. Central Command announced today that two of the three launchers that fired Scud missiles Saturday night were attacked immediately, setting off secondary explosions at one of the two. U.S. military officials declined to disclose where the attacks occurred, but it was understood that the two launchers that came under fire were in Iraq's western desert, aiming their missiles at Israel.

Partly as a result of the new missile-hunting tactics, they noted, the tempo of Iraqi missile launches against Saudi Arabia and Israel has slowed from 35 in the first week of the Persian Gulf War to 18 in the second week and three in the last four days.

Schwarzkopf, the U.S. commander of Operation Desert Storm, said Wednesday that U.S. and allied aircraft probably have destroyed all of the approximately 30 fixed missile launchers that Iraq was believed to have had when the war began Jan. 17. But an undetermined number of mobile launchers -- platforms on flatbed trucks -- escaped detection by moving between launches and hiding.

Schwarzkopf dismissed the Soviet-designed Scud missiles as "militarily insignificant," despite Iraq's modification for added range, since they cannot be aimed to hit precise targets. At the same time, he acknowledged that they are important because of the fear they inspire in the civilian populations of Saudi Arabia and Israel. Although all 57 Scud missiles fired on the two countries have been armed with conventional warheads, the fear has been intensified by a prospect that future missiles could be armed with chemical-agent warheads.

The two missiles fired at Israel on Saturday night, the 28th and 29th, landed harmlessly, Israeli authorities reported. Marine Maj. Gen. Robert B. Johnston said one of them may have missed Israel entirely, falling in Jordan, whose airspace Iraq uses to reach Israel.

The third Scud firing, the 28th at Saudi Arabia, apparently came from southern Iraq. It was intercepted by a U.S. Patriot missile over Riyadh, the Saudi capital. But chunks that landed in a residential neighborhood injured 29 people, chiefly from glass shards, Saudi authorities said.

U.S. military officers said the new quick-reaction tactics have created a situation in which Iraqi technicians are forced to drive to a launch site, crank the missile into firing position and take aim in the knowledge that, in the words of one officer, a U.S. air strike "could be only about five heartbeats away" once they hit the button.

Once the missile is fired, the Iraqi technicians are almost certain to have betrayed their location to an AWACS -- airborne warning and control systems -- plane flying within radar range. As counter-Scud patrols were multiplied over the last week, chances have increased that U.S. fighters are near enough to mount an immediate attack.

Destruction of the Iraqi network of Soviet-supplied antiaircraft missiles has enabled the U.S. jets to patrol more safely at high altitudes. Antiaircraft guns, which are still numerous, are more effective against low-flying planes.

U.S. officers refused to say whether they know how many Iraqi mobile launchers remain after the most recent hits. But they claimed the number has been reduced significantly since air supremacy was declared. At the same time, one officer estimated that Iraqi forces have enough missiles to last six months at the present firing rate, if the launchers are not all knocked out.