EASTERN SAUDI ARABIA, JAN. 19 -- It has begun as a high-tech spectacular, a first-ever live combat display of the latest in military technology. It has "smart bombs" that can pierce a building, blow up its command center and still leave the plumbing intact.

It has laser-guided this and radar-guided that, weapons of such precision that military targets can be detected, isolated and killed almost without collateral civilian damage, according to the accounts presented by U.S. officials. If there is such a thing as a "clean war," Operation Desert Storm appears to have discovered it.

And to hear U.S. military officials describe it, Desert Storm in its first days has fulfilled every expectation: heavy punishment for the enemy, minimum friendly casualties. With the war going so well for the allies, there has been a temptation toward euphoria, particularly among the pilots who in their first raids found very little to deter them except cloud cover over some targets.

But Desert Storm leaders, from President Bush and allied commander Gen. H. Norman Schwarzkopf down to unit commanders, have cautioned that the worst may be yet to come: "We must be realistic," Bush said at a news conference Friday. "There will be losses. There will be obstacles along the way. And war is never cheap or easy."

In what was perhaps a first look at a grimmer future, U.S. Marines on Saudi Arabia's northern border Thursday and Friday came under Iraqi small arms and artillery fire. Separate retaliatory attacks by Cobra helicopters and A-10 Warthog attack planes silenced an Iraqi artillery piece and mortar emplacement, killing an estimated 40 Iraqi soldiers, the Marines said. Two Marines and a Navy medic were wounded Thursday in earlier skirmishes.

The only publicly known blemish on Desert Storm's near-perfect record thus far has been the inability of allied warplanes to hunt down and destroy all of Iraqi President Saddam Hussein's mobile Scud launchers, which exploded at least eight missiles in Israeli cities Friday and Saturday. But despite its grave political potential, even this shortcoming has proved to be, militarily, a straw man. Israel reported extensive property damage, but only 30 injuries from the Scuds -- none serious.

Still, with the war three days old, the depth and strength of Iraqi fortifications above the Saudi border in occupied Kuwait remain largely untested. Pilots have given few details of their raids on these positions, so-called "soft targets" expected to be hit heavily from the air only after "hard-site" military installations, vital industries and other strategic targets in Iraq have been disposed of.

Iraq has more than 540,000 soldiers entrenched in the Arabian desert behind layers of sand berms, minefields, barbed wire, tank traps and other obstacles near the border and also in northern Kuwait and southern Iraq. Allied airpower hopes to dislodge them with bombs or induce them to surrender with leaflet drops, but this process, if it works at all, could take weeks. In Washington, Gen. Colin Powell, chairman of the Joint Chiefs of Staff, said today that allied air strikes "will now begin concentrating on the Republican Guard and some of the {ground} forces" in Iraq and Kuwait.

If airpower fails to dislodge the ground forces, U.S. and allied armored divisions will have the job of breaching the Iraqi line the old-fashioned way -- with tanks, artillery, infantry and sappers. The allies will have air support, but against a determined enemy the offensive would be dirty and deadly. Heavy casualties are all but guaranteed.

And despite the Marines' early sparring, the allies today are far from ready for a full-scale ground offensive. The 1st Marine Division and the British 1st Armored Division are in place close to assault positions, but the 2nd Marine Division is still moving forward and front-line Marine logistical and medical facilities are still being prepared.

Meanwhile, the Army VII Corps, consisting of three tank divisions, is not fully deployed, while other units are traveling northward to their jumping-off positions. The 82nd Airborne Division, light infantrymen expected to play a major role in clearing Kuwait City of enemy soldiers, broke camp this week to move closer to the border.

In all, ground forces' positioning and maneuvering could take two or three weeks, a period during which air power will likely carry most of the load. If Iraq's will to resist collapses beneath the weight of coalition ordnance, the allies could win in a walkover. If not, the war may take much longer, with casualties to match.

Another imponderable is Iraq's air force, some 700 aircraft strong, which has been little in evidence after a few token appearances. In all, the allies have registered 13 confirmed kills of Iraqi warplanes in the air or on the ground, although others may have been destroyed in hangars or bunkers hit in bombing raids, Pentagon sources said.

The absence of adversaries has puzzled allied fighter pilots and left them somewhat disappointed: "We know they're pretty conservative," said a Navy F-14 pilot who identified himself only by "Rake," his call sign. "But you'd think they'd have a change of heart. When you bomb the airfield they took off from, and you do it with impunity, you figure sooner or later they'd come back. But they just stayed away."

Pilots have reported Iraqi fighters flying up to meet the allied attack formations only to duck away when they got within radar range. Navy Cmdr. John Leenhouts, 40, executive officer of a squadron of A-7 light attack aircraft, reported "a confused evolution, flying back and forth," by the Iraqi warplanes. "I don't think they had a very clear picture of who was out there."

On the first day of Desert Storm, the pilots speculated that the Iraqis had stayed away in hopes, perhaps, of living to fight another day, but by Friday, the flyers were questioning whether that opportunity had come and gone. With many airfields badly damaged, with communications crippled and with hundreds of allied warplanes filling the sky above them, Iraqi air power was starting to become an abstraction.

"The first night the Iraqis shot pretty much everything they had," said Col. Manfred Rietsch, commander of the Group 11 Marine Aircraft Wing. "Since then we've had anti-aircraft artillery barrage fire. They are shooting, but not with much of a game plan of coordinating missile attacks."

"He's a formidable foe, but he's not formidable for us," said Col. John McBroom, wing commander of the 1st Tactical Fighter Wing. "It doesn't matter when we fly or where we fly. We're just going up there to take care of business."

Despite his tough talk, McBroom, a crusty 46-year-old Virginian, cautioned against overconfidence: "He still has weapons. He still has people up there. He still has an army up there. There is still a lot in Iraq. It just depends on what price he wants to pay, because he will pay dearly if he wants to keep going."

Another who urged caution was Army Lt. Gen. Thomas Kelly, senior operations officer for the Joint Chiefs of Staff, who said that "we are proceeding toward" control of the skies above Iraq. "I don't think we've achieved it completely, but we will in due course."

U.S. officials say their aircraft have "successfully engaged" about 80 percent of their targets so far. Pilots and journalists in Baghdad have reported the destruction of Saddam's presidential palace, the Defense Ministry, communications centers and military and industrial sites throughout Iraq.

But clouds have masked some targets, causing warplanes to turn back without dropping their bombs, and Saddam's ability to command his forces still appears intact, if the Scud attacks Friday and Saturday were any indication. One Air Force source said some targets may have to be revisited "several times," but expressed confidence that the allies have enough ordnance to destroy Iraq's strategic war-making capability, "no matter how long it takes."

All the visible evidence up to now suggests that the allies are having everything their way. From the first air raid over Baghdad, Desert Storm has been a mesmerizing, deadly sound-and-light show, much of it covered live on television or recorded in vivid detail by the participants. Sensors beneath an F-117A Stealth fighter showed a 2,000-pound laser-guided bomb dropping through a rooftop skylight to destroy one of Saddam's "presidential facilities."

Desert Storm has put much of the U.S. military arsenal on combat display for the first time since the Vietnam War. Reporters were allowed to visit the secret Stealth airfield for the first time since the crisis began.

The battleship USS Wisconsin fired dozens of Tomahawk cruise missiles into Baghdad early Thursday morning in the opening hours of Operation Desert Storm. "I heard the correspondents on the radio in Baghdad saying, 'I hear bombs, but I do not hear any planes,' " said an exultant Lt. Guy W. Zanti, the Wisconsin's missile officer. "That was because there were no planes."

Aircraft used cluster bombs to attack tanks supporting the Republican Guard, Saddam's elite troops, and destroyed enemy radar installations with HARM missiles. An Army air defense company blew up an approaching Scud rocket with a Patriot anti-missile missile -- right in front of an ABC television camera mounted on the roof of Saudi Arabia's Dhahran International Hotel.