DHAHRAN, SAUDI ARABIA, JAN. 26 -- After 10 days of bombing the communications and industrial targets that support Iraq's military machine, the United States and its allies are increasing efforts to break up the vast Iraqi troop deployments in southern Iraq and Kuwait and cut off their supply lines, military officials said today.

The shift toward battlefield attacks is designed to weaken Iraqi military resistance to allied ground troops, who eventually are expected to be called on to reclaim Kuwait, which has been held by an Iraqi occupation force since Aug. 2.

"The focus of the air war is starting to shift from strategic interdiction to more battlefield preparation," said Lt. Col. Mike Scott, a U.S. Central Command spokesman. Scott said the air raids are concentrating on military support and storage capabilities, as well as troops and armor spread across the Kuwaiti and Iraqi desert.

Officials said that while many of Iraq's facilities for making chemical and biological weapons -- and all of its nuclear production facilities -- have been bombed, the military is turning its attention to non-conventional weapons stored in hundreds of depots scattered throughout the battlefield. Some analysts and officials have said those weapons could pose the greatest threat to allied ground troops in the event of a ground war with Iraqi soldiers.

Although heavy clouds again obscured parts of Iraq and Kuwait, allied forces reported some success in today's air raids. A pilot involved in operations against the Republican Guard -- more than 100,000 of Iraq's best-trained troops, mostly massed along the Iraqi-Kuwaiti border -- reported seeing a massive fireball on the horizon 200 miles away, indicating that bombers might have hit an ammunition or fuel storage depot.

U.S. A-10 Thunderbolt "tank-killer" planes and Army and Marine attack helicopters also have been assaulting isolated Iraqi armor and artillery positions near the front lines in southern Kuwait, officials said.

Planes struck at transportation lines and railroad bridges, and allied forces claimed to have destroyed more airfields, staging new strikes against runways that Iraq managed to rebuild after attacks.

Along the Saudi border, U.S. Marines launched their biggest artillery attack yet before dawn today, firing about two dozen 155mm howitzers at Iraqi artillery positions six miles into Kuwait, field commanders said.

In another forward area, three Marines were killed and seven injured when two light armored vehicles collided as they returned from a raid along the Saudi-Kuwaiti border. The Pentagon identified the dead as Pfc. Michael A. Noline, 20, of Phoenix, Ariz.; Staff Sgt. Michael R. Conners Sr., 32, of Fremont, Calif., and Lance Cpl. Arthur O. Garza, 20, of Kingsville, Tex.

Cloud cover Friday limited the allied forces to about 1,000 missions, one of the lowest counts since the war began Jan. 17, officials said. An accurate count of today's flights was not available, but officials said the total number of sorties flown during the war stood at more than 20,000 as of this evening. Sorties have typically been divided evenly between bombing and support missions.

The cloud banks also continued to hamper intelligence officers in gauging the success of their air assault against Iraqi forces.

One Air Force F-4 Wild Weasel pilot reported after a flight over an undisclosed sector of Iraqi-held territory Friday, "There are more fires down there than I can count." But aside from such anecdotal evidence of success, military officials have been unable to gauge the air war's progress. The cloudy weather has obscured efforts to obtain enough satellite and reconnaissance photographs to assess the operation.

Even if the skies clear, as they did two days ago, judging the damage remains difficult. "You can't just look at the bomb craters and conclude anything, because the Republican Guard is dispersed," said one senior Central Command official. The impact "unfortunately has to be measured in weeks."

In the skies over central Iraq, U.S. Air Force F-15 fighter pilots shot down three of Iraq's Soviet-built MiG-23 fighter jets. Military officials described the encounter as a "fur-ball dogfight," the phrase fighter pilots use for particularly frantic air-to-air battles in which distinctions between friend and foe can be obscured.

Other allied aircraft reportedly destroyed three fully loaded Iraqi bombers as they sat on an Iraqi airfield, a spokesman for the U.S. Central Command said.

Iraqi pilots have made little effort to combat allied planes or to attempt strikes in allied territory. But since Friday, when a Saudi pilot downed two missile-loaded Iraqi planes heading south over the Persian Gulf, Saudi military authorities have been braced for another attempted air assault into Saudi Arabia.

Military officials say they have been perplexed by the lack of response from the Iraqi air force and said they do not know the extent of damage to planes that may be hidden inside fortified bunkers. "If he's holed up in bunkers, how good is he?" asked one senior U.S. military official. "Does he come out and fight?"

Scott, the Central Command spokesman, said allied airplanes were detecting no enemy radar on their missions. "Either they are not there and were destroyed, or they are afraid to come up because they will get destroyed. It's the same effect," he said.

Iraq continued to hurl Scud ballistic missiles into Israel and Saudi Arabia today, firing one at the Saudi capital of Riyadh and at least four at Israel. All five were intercepted by U.S.-supplied Patriot air-defense missiles, military officials said.

Senior U.S. military officials in Saudi Arabia said they expect Iraq to launch an intense barrage of Scuds into Israel and Saudi Arabia on Sunday during the airing of the Super Bowl because the attacks would get massive television exposure if ABC cuts away from the football game to report them. Military authorities said they also have detected a pattern of Iraqi missile launches timed to coincide with the airing of the U.S. networks' nightly newscasts.

In Washington, Maj. Gen. Martin Brandtner, the deputy for operations for the Joint Chiefs of Staff, said the military is "undertaking every conceivable course of action we can" to spot and knock out Iraq's Scud launchers, particularly mobile units that have eluded detection and are thought responsible for the launches against Israel and Saudi Arabia.

Despite the prospect of Scud-alert intermissions, tens of thousands of the 483,000 American troops in the Middle East are expected to tune in to the Super Bowl, which will air after midnight here on Armed Forces Radio. Said Lt. Col. Frank Waddel, a doctor assigned to the Air Force's 1st Tactical Fighter Wing's air evacuation hospital, "You need something to take your mind off what the reality is around here."

Staff writer Steve Fehr in Riyadh contributed to this report.